Some of the rumored and known options, not necessarily in order:
Starters
1A - Lester signing, 1B, Hammels trade, 1C Cueto trade, 1D Zimmerman trade, 1E Samardzija trade, 1F Shields signing
2A - Ross trade, 2B Iwakuma trade, 2C Latos trade, 2D Leake trade, 2E Cashner trade, 2F, Kennedy trade, 2G FA signing (many choices, but costly)
3A, Exercise a second of the choices in step 2
3B
1A - Sandoval signing, 1B Ramirez signing, 1C Headley signing, 1D in house option until mid season, 1E trade for Murphy or Valbuena
Bullpen
1A Miller signing, 1B Downs signing, 1C trade for LH reliever
In the best case scenario, they fit all the pieces together and retain the roster and financial flexibility they wish. Here's my suggestion:
Sign Lester @ 6/132
Sign Sandoval @5/90, alternate is to sign Hanley at similar numbers
Trade Napoli for Iwakuma
Sign LaRoche @ 3/45
Trade Craig, Webster and Owens to SD for Ross
Sign Miller @ 4/30
Start the 2015 season with:
Lester, Ross, Iwakuma, Buchholz, Kelly
Castillo, Pedroia, Ortiz, Cespedes, LaRoche, Sandoval, Victorino, Bogaerts, Vazquez, with Betts, Holt, Nava,and Butler/Lavarnway. Vic starts as a showcase for a trade
Koji, Miller, Tazawa, Mujica, Layne, Workman, RDLR
Hope to finish the 2015 season with:
Lester, Cueto (or other available ace), Ross, Buchholz or Iwakuma and Kelly. Assume Buchholz or Iwakuma dealt to obtain the ace. Johnson could be pushing Kelly for 5th spot.
Betts, Pedroia, Ortiz, Bogaerts, LaRoche, Sandoval, Castillo, Swihart, JBJ, with Holt, Nava, Weeks/Brentz and Vazquez
Koji, Miller, Tazawa, RDLR, Mujica, Layne, Workman, or Barnes, or Renaudo
Victorino and Cespedes will have been dealt in the mid year swap meet..
Going into 2016, it's likely one or two of the kids (Johnson and EdRod) are ready to take rotation spots, if not, there is a great FA market next year and they will have funds to use if needed. Swihart will have taken the starting Catcher spot and one of the kids back fills Mujica. So they could add 3, and possibly 4 more cost controlled positions to the 2016 roster. This allows the pattern used in 2015 to be deployed again. Start the year with a competitive, deep and flexible team that can trade veterans or prospects for needed parts mid year. The difference next year and going forward however, is they will have less needs, more available funds, and more prospects closer to ML ready. They would enjoy the same luxury going into 2017, and it would appear 2018.