Would you still go with that strategy with a flex position where you could potentially start 3 rb each week?
No I wouldn't. I'd prob want to secure 2RBs within my first 3 picks. I'd still be inclined to take a stud WR also though. The thing with a flex is that everyone becomes hell bent on starting 3RBs, RBs thus go off the board very fast. Don't reach for a RB just so you can play one in your flex. If there is garbage left for you at RB when it comes time for you to pick go WR WR. That's the beauty of getting a top 3 pick this yr, you can gamble on your 2nd RB because LJ/SA/LT are dominant enough to cover for a subpar player.
Don't underestimate the power of having a couple of stud WRs. I was in a league with Terpfan last year and he rode Steve Smith and Santana Moss all the way to the championship, his rbs were Bell and Gore.