After taking some mesurings of the table and bases, I've decided to use 1:15 scale.
That means the smallest battlion will still be about 18 figs, while I also get 24 and 30 fig battalions to.
The footprint will actualy be LESS then my 28mm figs, simply becasue of the baseing.
For my 28mm figs I base them on 40x50mm bases, That means a 24 fig battalion takes up 24x5cm, While for my 40mm I'll base them on 50x50mm, so the same 24 fig battalions only takes up 20x5cm, a good 40mm shorter.
At 1:15 a 18 man battalion would be 270 soldiers, while a 24 fig battalion would be 360, and a 30 figs battalion would be a wooping 450 soldiers.
I doubt any battalions will be any bigger then that