This team could go in a number of directions if they can get Martin, and depending on how they went about doing it. I would recommend trading someone other than Buchholz for Martin, sweetening the deal with someone like Bowden+ instead (who many believe will also be a very good pitcher).
If Lowell is one of those pieces and and Buchholz is not, and Teixeira could be added, then I think we have the makings of a complete team for years to come:
Ellsbury
Pedroia
Ortiz (-->Lars?)
Teixeira
Youkilis
Drew
Bay
Martin
Lowrie
Beckett
Lester
Dice K
Wake (future FA, Masteson)
Buchholz
An alternative would be to keep Lowell, not worry about Teixeira, and make a run at a SP like Burnett or Sheets or Vazquez (for Crisp+?) instead, and let them work from the lower third of the rotation where they can be coddled a bit more.
Ellsbury
Pedroia
Ortiz (-->Lars)
Youkilis
Drew
Lowell
Bay
Martin
Lowrie
Beckett
Lester
Dice-K
Burnett/Sheets/Vazquez
Buchholz
A third alternative might be to keep Lowell, move Buchholz (who I think could absolutely get the deal done for Martin: ...imagine Billingsley, Kershaw, and Buchholz moving forward with decent FA pickups from LA's perspective...) and go after a top notch guy like Sabathia or (if they still have enough talent, and he agrees) Peavy.
Ellsbury
Pedroia
Ortiz
Youkilis
Lowell
Drew
Bay
Martin
Lowrie
Beckett
Sabathia/Peavy
Lester
Dice-K
Wake/Masterson/Bowden?
There would be lots of choices because Martin's steady bat would add a fair amount of offense to that lineup for years to come (hopefully). The question would be whether getting that top notch starting pitcher is more valuable than the upgrade from a guy like Lowell to a guy like Teixeira.
Hell, it's hot stove season--these are not likely scenarios, but it's fun to play this stuff out sometimes.