well, i don't want to bother you but... are you SHURE about the 20mm?
I mean, it depends on what you want:
- if you want a big number of nice minis, maybe to not paint them or to fast paint, you can use 20mm
- if you want some small battlegroups, where the characters are full of personality, i really suggest to go with some copplestone or TAG or whatever 28mm ... more expensive, but really better!
- if you want the mass, you should go for 15mm... cheaper than 20mm metal (but not plastic!), and IMHO still as interesting as them!
I'm telling that because (Still IMHO) 20mm is the scale from which you start to lose personality in the minis: those are nice, but the faces are not so well defined, and the shades have to be made larger.
At that point, i'd go for 15mm... if you look on the forum you'll find PLENTY of those! i have some myself, i think that they are great... fast to paint and really interesting! I also have a lot of WWII 20mm, but i don't use them at all!
cheers,
Jack