I agree here......if you can get J.Nelson for R.Jennings I would do it in a heartbeat!!!
I love BMarsh this year and think he will be dominate but if you dealt FJAX you would be super thin (you would be rolling Martin and D.Brown at the RB position with no backups (I truly feel Hillis and Rodgers won't give you much value this year).....I do however think Blackmon is going to be a stud so you are good there and also think Washington will be fairly well off as well.....
I would say try the Nelson for Jennings and if not then stand pat as your team is pretty nice the way it is!
Good Luck m8!
Standard H2H 12 Team 1 Pt PPR, Start 1QB, 2RB, 2WR, 1 FLEX (RB/WR/TE), 1TE, 1K, 1 DEF