I remember you asking this last November
I've got the one friend I mentioned who I thought played both, but turns out he just does Bushido.
Sorry I can't help on the Kensei side.
Bushido is very playable and a lot of fun. I think that it helped that a friend and I learned it together so we were able to bounce rules off of one another in and out of games for better/faster learning.
I greatly enjoy the strategy behind Bushido especially the monitoring and taking advantage of a model's condition. In Bushido, when a model does an action of some kind, his condition worsens. Being tired isn't a big deal, but once you are exhausted, you are less effective in combat and that's when interesting things start to happen with alternating activation.
Number of models? Much like Infinity, it depends on what level you are playing at. This is determined by Koku/Rice to build your warband.
I think the standards are 36/42/50 for tournaments being much like Infinity's 150/200/300 in scope.
For my Ito, I usually have 4-5 models for 36 Koku, 5-6 models at 42, and for 50 I have had 6-7. That can vary depending on the cost of what I play, but I like to play some of the big nasty creatures of factions as the models are great and they have fun powers.