You can get small washers which are useful to stop the teeny models from getting knocked as much during play - these are normally pretty cheap if you buy a bag of them.
The last 6mm project I ever based individually was "travel Space Hulk" and it worked fine.
Waaay back in 40k 3E, I also had 3000pt 40k armies for many factions - all in Epic 6mm scale (so an army of that size typically cost me about £20) because the rules were streamlined enough that it was feasable. I even got as far as getting a scaled-down board too. Sadly the project remains tucked away in the attic, as I was then distracted by other things! Anyway, I planned to use 1" = 1cm as my game scale conversion, and whilst the models were a touch small for this, it meant the bases needed to be 10mm to stay proportional for gameplay purposes, and washers were again the best choice and value I could find.