The KeithsMoustache OffSeason plan would go as follows:

C:

The Diamondbacks have shown interest in a trade of Castillo for Snyder.  While Snyder might not be my first choice at catcher in a vacuum, this clears the second base spot while providing a 0.6 WAR catcher who can be a regular starter.  He has a respectable .347 OBP although not a lot of power, but this deficit could be counteracted elsewhere.  His primary purpose is to provide a serviceable starter and give us an outlet for Castillo to clear 2b.

1b: 

Signing Russell Branyan could be a good choice here.  He only made a bit over 1 mil last year, and after putting up great numbers this past season, I could see offering him ~5-6 million with a club option for 2011 in the event that Davis isn't ready to take over 1b duties by then.  If Branyan was averse to a 1 year contract, we could offer two years, but I wouldn't go any further so we could keep things open for Ike in the near future.  Branyan posted a UZR of 2.4, and an OPS of .826, both respectable numbers.  He gives us some of the pop we need at 1b with 31 HRs last year.  He posted a WAR of 2.8 this past year.

2b:

Placido Polanco is at the top of my 2B wish list.   Posting a WAR >3 the last 3 seasons makes him a valuable and consistent second baseman.   He provides a solid bat for a middle infielder with a .727 OPS, and defensively would be an enormous improvement with a UZR of 11 last year.  His presence would also greatly aid the pitching staff, especially Mike Pelfrey, by providing better infield defense.   I think a 2 or 3 year (preferably 2), 6-7 M/year deal could be worked out for him. 

OF:

I'm going to stray a bit from the pack here, and not discuss Holliday.  He's a great player, probably the best out there as a FA right now, but we need to upgrade at multiple positions and his pricetag is prohibitively expensive if we want to fix all the leaks in the ship (again have to take things outside of a vacuum here). 

Instead I suggest we sign Mike Cameron to play center field and move Beltran to left field.  This serves to protect our pre-existing investment in Beltran, who has shown a few signs his knees could be a problem in the future.  Cameron posted a UZR of 10.3 in CF this year, along with 24 HRs and an OPS of .795, a value which he has maintained throughout most of his career.  I would value a contract for him around 2 years, 9 million per year.   

I would use Angel Pagan as our right fielder, after posting a 2.8 WAR season in which he had an OPS of .837.  While I expect a bit of coming back down to earth from Pagan he has shown he can handle a starting position in the outfield and has a good enough bat to sustain himself at this position especially with Beltran and Cameron in the OF.  Defensively this would also be an amazing outfield, which is a necessity in the expansive Citi outfield. 

Starting Pitching

There's one acquisition I would like to see made with regards to starting pitching, which is Joel Pinero.  While I know Pinero's numbers won't maintain the amazing 3.27 FIP, 4.8 WAR he put up in this year, I believe that his new sinkerball will be a valuable tool which will allow him to keep his FIP below his previous career numbers.  Batters will adjust to his new pitching style, but I can still see him posting a FIP of around 4.0 (Bill James predicts 4.2) even after this happens.  He also pitched over 200 innings this year, which would be a huge help to a Mets bullpen that has gone overworked year after year for the last 3 or 4 years.  Pinero would likely cost 10 mil per year for a 3 year deal.

I would offer Maine a 1 year, 3 million dollar contract in order to compete for a spot in the rotation along with Figueroa and Niese.  If Maine were unable to lock down a starting job in spring training he could still be a valuable asset to the bullpen or vice versa.

Bullpen

The only signing I would look to make to the bullpen is Kiko Calero.   With a 2.56 FIP last year he could be a great setup man if he can stay healthy, and those same health concerns will keep his value on the market reasonably low.  I think 2 years at 1.5 million per year could be enough to snare him.

Other notes:

I would add Endy Chavez as a 4th outfielder on a 2 year, 5 million deal, he can play every outfield position, hits well, and come on, if you're a Met fan and you don't miss this guy you have no soul. 

I also give Ollie the benefit of the doubt that he'll bounce back to a serviceable pitcher this year, and I think Pelfrey will have a much easier time with a second baseman and shortstop with some defensive skills behind him. 

My final team would look something like this.

                                                          Pos               Player                  Cost (M)

Final Payroll ~135.5 million.

This keeps payroll at around the same level it has been recently, leaving room for the all important 2011 season when a lot of our big name players are free agent eligible.   I think this plan sufficiently addresses the holes at first, second, and outfield, improves our bench, and improves our starting pitching not only by addition of a pitcher, but by vastly improving our defense.  The improved pitching will impact the bullpen by forcing us to use them less, and the addition of Kiko Calero would add stability to the pen by providing a defined setup man.  Other relievers could then be better deployed situationally.