Given the lack quality at SS this year, I would certainly add Alexi Ramirez as your 7th keeper. He also as 2b elgibility in many leagues as well which makes him all the more valuable.
As for the last 3 spots, a lot depends in what happens in free agency and trades. I could see keeping Butler, Snider, Stewart or Burrell. Also, from and SP perspective, Maine, Johnson, and Harang merit consideration
As of right now I would select Stewart, Burrell and Maine.
Stewart - I think they will find a way to get him in the lineup, whether it be 3b, 2b, or OF. Helton is a lock to need time off, Atkins on trading block, GM O'Dowd quoted recently they might play Stewart in the OF now that Holliday is gone. I think he plays. Also, 11 games at 2b last year, so he might qualify at 2b in your league as well. I like him better than Snider and Butler in terms of both upside and getting a chance to play.
Burrell - Stewart is you risk/reward guy, so I would go with the proven commodity for the last hitter spot. Of course, my opinion could change depending where he ends up.
Maine - I think he returns to 07 form. Had a bone spur removed from pitching shoulder, was not a rotator cuff or tendon type situation. Has a better opportunity for W's once Met revamp bullpen in offseason than other two SP choices.