I've thought about using my Warmaster Ancients armies and with the new rules that allow 20mm on most infantry I think it will work. Warmaster are 10mm and 20x40mm bases.
For massed infantry, I typically do 10 figs per base (5 and 5) and they fit tight but look good. For light horse, I do 2 based with 4-5 (that would be for 40x40) so I'd think 4 would look loose enough on a 30x40. Generally, I does seem like double will work, but I'd consider doing 10 on a 20x40 for the heavy infantry.