Established Dynasty Draft - When to Select FA over a Rook?

I have the #11 by round, and do not have a second rd pick. My RBs are old - Blount, Lynch, Chris Thompson and Gurley. Is it worth using my 3rd or 4th rd picks for McKinnon or Alex Collins? Josh Gordon is available.

Took over an awful team - 2nd year in the league and am thin at RB and WR.