As for the amount of units per tile and bombardment ranges, I think I may have thought of a nice solution. As archers/boats/early-mid game siege weapons can bombard 2 tiles away and the late siege/boats/Longbowman can bombard 3 tiles away, might I suggest a combat type 1UPT. In history the archers and melee were never too far apart and the siege were always behind those. I have in mind making a system where certain units can combine with certain units, keep the 1 unit per tile rule but make certain units be able to share the tile with other certain units. If melee shared the tile with archers, we could make the archer range to 1 tile and the longbowman range also to 1 tile but with a different perk - like more accuracy or slightly more damage. The siege units would keep their 2-3 range bombard respectively and therefore would be able to set up the field a little more casually with more room for everything without sacrificing the tactical point of view. Melee and archers could share a tile, tanks and infantry could share a tile, mounted units can share a tile with almost everything. However only 2 units should be able to share a tile at the same time, you can't have an archer melee unit and horseman on the same tile - that would more or less defeat the purpose.