how many games could fit on a 8gb usb hdd?
Depends what games you want to put on it. after WBFS removes all the useless stuff games can range from like 100mb up to 4gb.
For example NSMB takes up ~350mb, while rockband 2 takes up ~3.5gb.
Would need to list the games you want to put on so people can give you a rough estimate of their size