Basing for any rules system is up to you; however, the CF rules suggest:
3 figures for a rifle or SMG squad on 1-1/4" by 1-1/4" base
2 figures for an HMG stand on 1-1/4" by 1-1/4" base
Company commanders, 2 figures on 1-1/4" by 1-1/4" base
Platoon commanders, 1 figure on a 5/8" by 1-1/4" base
I personally use 1-1/2" by 1-1/2" bases for my 1:72 stuff and usually put only 2 figures on a base – I find this looks more believeable as far as spacing goes and I'm too lazy to do the extra figures if I were to do three to a base. I use copper clippings around the base to represent machine gun stands:
MG stand and a Company Commander stand: picture
Behind the Stug is a company commander (left) and a smaller platoon commander stand (I just cut stands to be smallish for PCs, I don't bother to measure the size): picture
From left to right, a Soviet SMG squad, a plaatoon commander and an MG stand: picture
You'll need to be able to distinguish what stands belong to what squads. The rules recommend labels on the top of the base. I felt this detracted from any mini-diorama look so for years, I used to use coloured stickers underneath the stands to mark what squads belonged to what platoon, company. I now prefer to use the edge of the base as per: picture and here's an example of that, see the British stands to the left: picture
All these pics are from my web page at ucs.mun.ca/~tmarshal which has loads of battle reports with loads more pictures of my squads.