So a person wants Peyton Manning from me?

This is seriously weird. The only reason you make a trade is if it improves your team. You didn't give league size, so we have no idea if there might be better starting QBs out there than Fitz.

If you need help at RB/WR, the only way to get it using Manning is to do a combo trade. You'd offer up Manning and one of your RB/WRs and in exchange you'd get a startable QB like Rivers, Romo, Stafford, etc and an upgrade at RB/WR.

You don't say who this guy has at QB, but if he's a minor downgrade then propose the deal. If not, you can't go through the rest of the season with Fitz as your starter. It doesn't matter what the other guy wants.

It depends on your other qb and other players you have. But if you have a solid backup, Calvin Johnson or Lesean McCoy and Allen or Edelman.

Since you aren't telling us the league structure (it's obviously unique if you are OK trading Manning and leaving yourself only Fitzpatrick) that's sort of hard to say, isn't it?

Right now my backup is Fitzpatrick. And really I just got him because Manning was on a bye last week. This league is very flex heavy.