Any suggested house rules to make the game more challenging? (VI expansion)

[Clifton]

So I have been playing MTW off and on since its release in 2001 and have recently picked it up again for the first time in 5 or 6 years. I tried the English on Hard at first this time around and rushed through the entire map. Next was the Danes, who were even easier to win with due to Longboats (trading is broken for the player), Vikings and especially the easily obtained yet insanely OP Viking Huscarls. Next came the Hungarians on Expert, I decided to pick them and go for a style I wasn't used to - the Szeleky and other cavalry to make a 'mongol-style' army, this time I didn't even bother reaching the 60% point as it was already an obvious win before most enemy provinces were able to produce even half-decent units.
So I thought it couldn't get much harder than Expert Russia in the High period (all previous had been Early starts), especially with there being only 26 years before the horde arrives. But both Muscovoy and Novograd have fortresses and can already produce Halberdiers, only 6 years away from Arbalesters, whilst conquering Livonia and Lithuania nets you a province that can train Halberdiers and Arbalesters straight off the bat respectively, so building elite armies quickly is an easy task (especially with the already in place 80% farming in your rich provinces and easily conquerable steppes). It wasn't long before the horde was wiped out (and half the battles weren't even river crossings - forests will do just as well), I'd conquered Poland for attacking me, broken Germany in half, humiliated the Hungarians and started to push into Turkish territories. Now to be honest this is the most fun game so far and I'm taking it more slowly than usual, but it's still too easy, especially now I've realised that Arbalesters are so insanely good with 2 valour or more.
After each campaign I put in a new house rule;
After England - No mercenaries
After Denmark - No mercenaries, No Trade
After Hungary - No mercenaries, No Trade, No awful units like Peasants, Urban Militia etc for garrison duty
After High Russia - what do you suggest?

I was thinking of going into the script and preventing Peasants and Urban Militia from being able to be built by anyone as I've seen an easy to understand guide online on how to do this, and this will prevent the opponent bankrupting themselves with crap units. Another Idea I had was to stop myself from picking a faction which has very good fort units from the get go, eg: Almohad Urban Militia, Szeleky, Vikings, Highlanders, Gallowglasses, Byzantine Infantry (yes - a keep for the last one I know, but you get the idea), etc. But not using Urban Militia/Slavs/Javelinmen/Peasants etc. But what faction could that be?

So what other house rules to people use, without using an entirely different mod, to try and give the AI a decent chance?