16GB can be not enough, as right now my windows folder has 16.2GB after 3 days of working on win8.
it is still without any user files, programs etc.
however, wtg seems to support 16GB drives (this is minimal requirement) and i won't expect enough free space after putting whole system on it.
so you will need 32GB drive (at least).
MS is highly recommending USB3
if u looking for a fast and reliable USB2 drive, that have a big chance of handling it, try patriot XPorter series. i',m using them all the time. (the first one that i got was xporter 8gb. its 4 years old now, visited interiors of washing mashine 3 times, dropped from 30meters!, used as pvr etc, still works like new)