I think it would work fine without grids. I will try it without a grid as it means I could reduce the movement unit a bit and get better use of the limited space I have on my table at home. In that instance, I think ZOC would just be base-to-base contact, or possibly a very small 3cm zone or something. I do think that square unit bases would be better in a grid-less game, as there might be some issues with turning otherwise. It's probably not a big deal, but worth bearing in mind.
The army generator needs a bit more work I think, but it was primarily for setting up pick-up games.
I think you would eventually want the ability to have different combat values for units, just to be able to play different battles. But our initial games just lifted the combat values straight from sections of the battles in the board game. I liked the idea of having the figures themselves translate to unit stats, but in practice this was a bit tricky trying to count them before each fight. It would be easier in 10mm though!
Finally, I would say that time spent on planning the bases is time well spent. With mixed figure bases, the more figures you use the better it looks, but you need a lot of bases for Tenkatoitsu. Even with 30 figures on a base, you're looking at around 500 figures a side. That's a lot of painting. Also, the bigger the base, the better it looks, but larger bases cut down the size of your battlefield in relative terms. So it's important to get it right before you start.