This is my first time playing FF so I'm a little in the dark when it comes to the strategy of this... We need WR, QB, RB and the like yes? The idea is to have multiples so you can choose who to start right? Does wanting multiples apply to defenses as well?
Multiples definately applies to Defenses as well, as you have to CYA on bye weeks. It sucks to have no replacement and get a big zero when your defense is on a bye week.

It's a godd idea, but not a requirement, to have multiples for all positions to cover those nasty injuries and bye weeks. For 20 players, most ppl would draft:
2-3 QB
3-4 RB
4-5 WR
1-2 TE
1-2 Kickers
2-3 Defense
Just a rough outline of what you newbies should look for
12 Bench players seems like a lot, but with so many injuries and bye weeks, it'll really come in handy.
Jeff