Did you stick the flock mat to a board or just laid it on the table?
Kallistra also carries a line fo 12mm minis, its grown since the last time I checked. You can see some pics for their minis with 12mm buildings.
I would have gone with 6mm buildings too, not sure how it’ll look since they varie so much by manufacturers. Pictures of 10mm minis with 6mm buildings at bottom
This reminds me, Warmaster is 10mm. You could potentially use official GW minis, if you have a small fortune stashed away somewhere.
From experience, any minis will fit nicely on a base equal to or greater than its scale. I’ve based 10mm/12mm on round 12mm base before and it works fine. Personally I’d base 4 minis on a 20mm base and keep all the rules measurements. Heroes probably be single if on beast, foot heroes will have retainers. It’ll look more epic and ranges look more realistic, but that’s just me.
Tired is enough.
I like tiny miniatures