This is what I tend to do
Heavy foot I use 40x20 bases ( they were already based like that and it was too much to change to 40x15, plus they look better in 40 x20 cause you can fit two ranks )
in those bases I can fit two ranks of 6 old glory ( 12 per base total ) or two ranks of 5 Militum ( 10 per base total )
Medium foot I am planning on having 8 per base ( two ranks of 4 ) the problem is with Old Glory. Old Glory minis come in strips so for example my scutarii from old glory ( which I personally like better than the militym ones ) are so close together in the strips that I still have 12 per base. But when possible I'll keep to 8 per base for medium foot.
Light foot I tend to have about 5 or 6 per base in irregular formations
light horse I have 3 per base
cavalry I have 4 per base
all my horse are in the correct 40x30
I was using warmaster before so my elephants are in 20x40 bases and I thought about putting two together for the 40x40 of FOG but I didn't like the look, instead I did some magentic extensions to my bases and now I have one elephant per 40x40 base and I like how they look.
( I also had to do magnetic extensions to my 40x20 cav to have them in 40x30 , so at the end of the day I can use my armies for both systems, though it is very unlikely that I would play WAB if I have enough time to play FOG )
ok, so that is how I base
cheers
Seldon