Thank you again for all the replies; they have been very useful. My second campaign, as Chosokabe at Normal difficulty is going quite differently than my first campaign. While my first campaign was all about building stacks and expanding militarily (until the dreaded Realm Divide blew up in my face), this second campaign I have followed the philosophy of:

"The nail that sticks out gets hammered down."

Recalling how useless Sanuki, Awa, and especially Awaji seemed to be, I traded with Soga and Miyoshi instead, and allied with Soga (based on their performance, a sad decision).

I liked the Aki-Bingo-Bitchu-Bizen-Harima axis from my first game: good provinces with nice resources, and easy to defend, but by the time I was ready to cross the waters, Aki was taken by my ally Ouchi, and Harima seemed a bridge too far, as Bizen seems much more important, and easy to defend. So currently I have Tosa and Iyo on Shikoku, and, since about turn 16, Bingo-Bitchu-Bizen, a nice, compact territory.

My plan has been to max out Bizen, and until then, delay maintaining a large army I wasn't using. I was starting to worry that I was surrounded by friends, or allies of friends, and there would be no easy targets for my high quality army, but just at the right moment, around turn 28, Ito, having conquered Kyushu, declared war on Ouchi, and I was pleased to join in. That's where I am now. I am thinking of aiming at Tsukushi, Higo, and Hizen, which seem both defensible, have useful resources, and will help me to defend my trade routes. That's the plan, any way.
Quote Originally Posted by Feelotraveller
With Chosokabe you will usually have to pay a fair bit to get trade agreements (on normal I tend to pay in the region of 1000-1500 koku, lump sum). You have both wood and stone early (and horses from Miyoshi soon after) and the AI is pretty smart about trade agreements; they know you will benefit more than them.
By starting trading on turn 1, with both Miyoshi and Soga, trade partners have been easy to acquire, and I haven't paid more than 700 for an agreement, and usually much less. I am very impressed by the money made by trade. It's certainly comparable with conquering new provinces, and has several advantages. Mainly, that I don't find my self with a large army to maintain, then looking for new conquests to justify the maintanance of said army. I've kept a much lower profile this time around.
Quote Originally Posted by Feelotraveller
There is no limit to the number of trade partners a clan can have.
Well with only four trade ports, it seems I can only have four trade partners.
Quote Originally Posted by Oh! TheLast Days!
Don't use marriages for mere trade agreements though. Wait until you know who you are aiming to win as a long term ally and marry off your children to them. If you really don't get trade partners because they are all tied up already try using the diplomatic option of "Demand Trade Embargo" where you basically ask them to break a trade agreement with a trade partner. You'll have to invest money again though.
So far, so good. I haven't married off my daughter yet. I was hoping to use her to secure Miyoshi until Realm Divide, but they seem uninterested. On the other hand, they really are peaceful. I am sure they will betray me eventually.

Speaking of which, how much can or should I rely on the numeric attitudes of the clans? If Soga is Ambitious, Reliable and Very Friendly, how likely is he to march on my capital?
Quote Originally Posted by Nowake
Tips for improving diplomatic relations: sue for peace a couple of times in the beginning. This will give your daimyo the trait Peaceable, which gives you +10 to diplomatic relations.
That didn't seem to work. After I conquered Bingo-Bitchu-Bizen from the much disliked Urakami, I offered peace to them and their Bessho allies, leaving them with much reduced armies. Maybe if I were conquering one province, then suing for peace, or not conquering any, that might work, but to be worth the effort of going to war, I'd like a few defensible, useful provinces for my trouble.

I've avoided the vassal route this game so far. My understanding is that it effects your reknown as much as conquering, and besides the pathetic Soga, I've not seen any good candidates. Maybe in this coming Kyushu war with Ito.
Quote Originally Posted by Nowake
You will have discovered all the clans, as I described above. Search for whoever has daughters. Marry them. Don't hold off, just go ahead and marry them to retainers and what not. It's all in creating as favorable a climate as possible for yourself -- note that there are diplomatic penalties to be had with clans which are in open conflict with the one providing the bride
Haven't married anyone yet, I think I'll explore the possibilities. I was hoping for clearer lines to the East, so I could pick a side, but instead it's a mess, with the two clans I fear the most allied with each other.
Quote Originally Posted by Nowake
Just hold on, build your economy and play defensively. Make sure you have a decent warchest (100.000 koku or so) and 3 to 4 army corps before you trigger the realm divide -- or that your revenue cannot plummet too much (and it really shouldn't if you play it right and capture all the trade nodes beforehand -- you really should, even during realm divide, the income you receive "from unsold trade resources" will keep your revenue going; about 11.000 koku from those unsold resources if you keep all the trade nodes -- the AI is not very effective at raiding you once you defeat a couple of its fleets.
Really? A hundred grand? I'd better keep taking it slow. My income seems not impressive enough, but I need to absorb another three provinces now I think. By focusing on max-ing Bizen as soon as possible, my Chi arts have suffered. On the other hand, I've not been maintaining a large army, and only now am I building it up. The war with Ito will be the ripe fruit that falls into my open palm.
Quote Originally Posted by Nowake
Well, yeah, of course, I was talking about your options, but every koku matters. It's situational and preferential, I somehow pace my recruitment very tightly.
Avoiding or deferring unit maintance is about the most effective thing I've found to grow my economy. I try to build as few units as I think I need, and disband any units inferior to what I could recruit. That's why I rushed to max out Bizen, so every unit I recruit has bonus XP, melee and armor. Initially, I am focusing on Ashigaru, but I expect to feed Samurai to the meat grinder eventually.
Quote Originally Posted by Nowake
So, to merge them, simply drag-and-drop the heavily damaged unit's card (on the campaign map, not on the battlefield) over any other damaged identical unit i.e. if you will drag-and-drop a unit of 20 Yari Ashigaru over a unit of 190 Yari Ashigaru (playing on Ultra unit size, a YA unit has 200 men), you will then have a unit of 200 Yari Ashigaru and one of 10. If the number would be 180 or lower, the unit would be fully absorbed. And of course, note that each Yari Ashigaru in each unit has its own experience level, so the damaged unit will raise or lower the experience mean during the merger.
Or select the two units, and hit CTRL-M.

Are you saying that I can merge Yari Ashigaru units to become 180 men, instead of 150, at the same maintance cost? What happens when they lose men? Do they replenish back to 180, or stop at 150? What is "Ultra Unit Size?"
Quote Originally Posted by Madae
Other things to keep in mind; I try not to trade with enemies of my friends. I'm not sure if that even matters, but I would like to think it does.
I have a theory that if you attack a trade partner, either your trade partners, or their trade partners, or both, consider that to be "Dishonouring Treaties." But I don't understand how the various diplomacy modifiers seem to come into play. My good allies the Ouchi for some reason all of a sudden decided I had been "Dishonouring Treaties," and I had done nothing to anyone. The Ikko Ikki broke a trade agreement with me, but that's all I can think of.
Quote Originally Posted by Madae
Also, when expanding, it's a very good idea to take a few settlements and then hold off and defend for awhile so that diplomacy penalty subsides. It won't be there forever, and you have plenty of time to win the game. Don't feel like you have to steamroll every province you run into as quickly as possible. Wait it out for more positive benefits. You'll want to have an assortment of friends or vassals by the great divide anyway, so you still have avenues of making money when other clans start teaming up against you.
That's been the plan. I took Bingo-Bitchu-Bizen, and have been peaceably building them up for a few years. My expansion penalty is only a few points now. I intend to do the same thing against Ito in Kyushu: taking Tsukushi, Higen and Hizen, then settling down again for a few years. I figure if I average a little under one province a year, I will keep a low profile, and steadily move towards the win.

What I am hearing is that I should probably make a vassal during this coming war as well. I did notice that you can trade with vassals, which I'd thought otherwise.

Thank you for the advice about Field Battles, Madae. For now, I am relying on Auto-Resolve on the theory that once I master the economic game, I can more easily afford the army I'd like to play with.

Again, thank you all for the advice and insights. I am really enjoying this game, and this forum.

Smeelbo-san