You should definetly have at least 2-5 stacks plus garrisons. A couple things to consider:
1) Are you maintaining mercs in your armies? They're super pricey so you should only hire them for short periods of time.
2) Are all of your garrisons free? Units are only free to maintain if they are recruitable in that castle, so having Dornishmen garrison Highgarden will charge you upkeep.
I'd say it is a bit closer to vanilla in terms of battle speed and difficulty. As for recommended difficulty, I'm actually a bit iffy on what those actually do. I think Battle Difficulty only affects Auto-Resolve, so I'd just leave that at Medium. As for campaign difficulty, it depends on how much you wanna fight. In my experience VH will mean lots of enemy stacks to kill while Medium is a more low-key experience. Again though, I'm not really sure what the exact effects are. Can anyone else enlighten us?
Also, some previews!
First some Thenns:
And, of course, the one you've all been waiting for: