I don't like the trade. Although Carson has been putting up some good numbers due to all that garbage time, Drew Brees is a model of consistency and will give you 20 pts minimum every week. Trent Richardson is a beast and although not a fantasy super stud like Arian, he's still extremely consistent. He must be part of 50% of the Browns offense.
The problem I have with Arian Foster is at 10-1, the Texans have already pretty much clinched the AFC South and possibly the AFC in the next few weeks. They'll definitely sit Arian and/or limit his carries.
I understand you are trying to upgrade your WR core but I'd rather keep Brees.