There are 3 types of bases in FoW.
Small = Used for 1-3 infantry, such as command stands, light mortars and man packed weapon teams.
Medium = 4-5 infantry per base, regular infantry teams are based upon these. As are small AT guns, HMG and medium mortar teams etc. Cavalry command is also based upon these.
Large = Used for large artillery and for basing cavalry (4 per base).
The book will tell you how many infantry you will have in each "team" , you could go either by the book and base 5 infantry where the book tells you, or cut corners and base them 4 per base. Does not make any in game impact whatsoever. Though I guess some nerds might get angry at you for this but as I said it does not impact the rules. Usually you have an equal amount of 5 and 4 man infantry teams within your platoon.
If you want to be 100% sure you should wait until you get the source book for the eastern front.
I based my Polish scouts with only 4 infantry per base to make them easier to pick out on the table and to double as dismounted cavalry.