Well in regards to the core players thing...the Rams traded 2 90+ players earlier and I just recently traded my 2nd 90+ player so I think we are saying 4 core players is allowed this season.
In regards to the trade...it's tough to make a call on this one. I have the same concerns as BV, but the way I see it...the Ravens aren't losing much in the trade since they aren't even using Ed Reed, but the Bills are gaining a LOT in the trade. So I don't really know how you would make the call on this one. McKelvin and Foxworth are both 93 speed so speed isn't even a factor...the only major upside is McKelvin's 9 point superiority in man coverage, which will probably help out a good bit...although I'm not sure I would say that 9-point difference in man coverage is enough to want to go through with the trade.
And in regards to the draft picks...I find a 2nd round draft pick to be a lot more valuable than a 3rd + 4th. I think once you get to the 3rd/4th round of the rookie draft, chances are that the player you pick up isn't going to be good enough for you to start on your team. In the 1st and 2nd round, you can easily find a player with a high enough caliber to be starting on your team. So in MY opinion at least...from the 3rd round onward, you're really only looking for depth at whatever position you draft. Those players aren't really going to be high-impact players, at least not until they progress over the course of a season or two.
Still, despite my concerns...I give my support for the trade.
And regarding the age difference (34 or 32), I think the website adds a year or two to what a player's age really is (in most cases). Then there are the rookies who are just completely f'ed up in regards to age...