Sounds exciting!

I like level variability ideas in particular. In that sense, as a suggestion, I think a system of level prefixes can increase replayability even further, slight chance-based generation alteration, like prefixes that:

• may changes level mostly visually (Empire meets New Year, so there are snowmans and snow everywhere, or Halloween with pumpkins, etc);
• or affect gameplay slightly (like make half of buildings wooden and therefore fragile or opposite, or spawn magical defensive crystals that debuff your abilities like making them more costly, or shot you each time you cast (would be even funnier if some empire wizard could be friendly shot with it) )
• or affect types and quantity of particular mobs (spawn camps with additional archers around map, or maybe regenerate entire map in forest archer outpost style where 80% of units turn into archers, and water tiles turn into tree tiles)
• or something small and special, like spawn specific witch house with it being miniboss which focuses on debuffing you to death and deals poison damage, or spawn sacrificial altar place, interacting with gives you a squad of 5-10 skeletons.
• maybe something that alters level structure significantly, like a very big part of map regenerates as a palace with royal guard inside and maybe some additional (forced/unforced) goal related to that.

like biome modifiers from Noita for reference :) or disasters/mutators from Streets of Rogue, or Level Feeling from Spelunky.

Thanks for detailed answer!