First off, for your QB, I think it depends on what size league you're in. If you're in a 12 or 14 team, I think I'd be ok with Flacco. He's has great upside, especially with the addition of Lee Evans to that Ravens offense.
I agree with B3N1ZJAMIN, if you were planning on drafting WR heavy, I'm not sure why you would want to change things up now that the draft is over. Best, Lynch and Thomas aren't bad RBs, they're just not studs. If it were me, and I wanted to really add some strength, I think I'd put Andre Johnson on the trading block. I think someone with a weak WR corps would be willing to ship off a stud RB, or 2 more descent ones for AJ. That would still leave you with Wallace, Marshall & Nicks which I still would be very happy with. Just in playing around with some trade options, you could might get a McCoy, Gore, Mendy, MJD, etc.
I just think you would get the strength at RB that you want by trading off Nicks or Wallace. If you traded one, this is going to give you another RB comparable to Best, which I don't think you want.
Best of luck!