You know I can answer some of these question via my reading of everything CA members have said and my studying any screens that come along.

3. will one still be able to go thousands of miles across a sea to invade in one turn?
4. if not, how will it work now?
Moving armies by sea is more dicey now as you have to load the army into ships and send them on their way. Taking how ever long it takes the ship to get from point A to point B. If your ships are lost the troops on them are lost too. Strategic agents are moved this way now too with the same risks.

1: Land Based Trade - does it produce? In MTW the trading was almost entirely sea based and if you wanted to build a trade empire without ships it was an oxymoron. I seem to remember the Silk Road bringing in many goods throughout this timeframe and bringing the trade from the East certainly brought a greater economic benefit to the European based factions which were able to exploit this trade. Will Land Based Trade be improved at all or is trade in general being revamped in any way?
4. What does land based trade involve? Is it just as profitable as sea based trade?
Land and sea basd trade have little indicators know on land there are little lines of camels going from city to city same with sea trade you can see little trade ships plugging along between ports.

5: We've been told about the diplomacy system. Can you post a list of things which can be asked for of another faction as well as the list of things which can be given in return?
I've seen a screen of the diplomatic negotiation screen it had the offer/demand settlement option up but there were others further down. that were a bit blurry, lots of them but blurry.

1) There are two seasons. Are turns keyed to seasons, or will there be multiple turns per season?
Some person from CA said that the turns are based on seasons again 2 per year summer and winter.

Now that I have insulted everybody with my hubris my questions.
1.To load a full stack army into ships will you need a full stack navy?
2.Can you only build forts in specific places or can you plunk one down anywhere that strikes your fancy?
3.Has the mercenary system been changed at all?
4.How many surgeons, spies, priests can you have in a generals retinue?
5.How far can an army go in one turn?