Welcome to WebmasterWorld Guest from 18.104.22.168
As far as PR, even 4-5 good (PR6, 5) links can bump you to at least PR4.
one of my sites has only 10 inbounds (natural and strong) and it has a PR5. millions of sites out there with 100's of IBL's and still have a PR on the low end of the scale.
concentrate on a few on-theme quality PR links to get you going in the right direction. time spent on quantity will be a waste of time.
Less that 10 links from PR3 sites is enough to get PR2, in my experience, but of course under condition that these sites haven't too many outbound links.
One is enough, though.