I think you can pencil in Voit at DH, so I think you have 4 or 5 regulars lined up. Meneses will be in right or first, Abrams, Garcia, and Ruiz as the primary guys up the middle, and probably Thomas as one of the outfielders, position TBD.
3rd they probably do not go outside the organization with Kieboom and Alu competing with Vargas. Vargas is arb eligible for the first time and will be given a contract primarily as a backup IF but also the emergency 3rd baseman if neither of the home grown guys run with the job from the start of spring training.
I can signing a guy who can be the 3rd man in the 1B/DH/RF combo. A first baseman pushes Meneses to right, which leaves Thomas possibly in CF or LF. In that case, I could see something a little weird, with essentially Yadi and Robles platooning, with Yadi in left, Thomas in CF against RHP and Robles in CF, Thomas in left against LHP. Defensive subbing late with a lead. This way, we only look for one outside the organization position player, probably for 1-3 years. Figure things go right, Hassell maybe by August takes over CF or RF.
I don't see a huge need for bullpen upgrades. I think that a bottom tier team can get by with Finnegan / Edwards / Harvey at the start of the year, perhaps bring back Doo for minimal cost if the repair works on the elbow, hope to give a shot to Cronin and Brzycky as well as Ferrer and figure that at least one can help, bring back Arano and Thompson for middle innings and lower leverage, and keep Espino as a long guy along with perhaps Fedde. I don't know if Rainey will be back next year, but he is also an asset assuming a normal recovery, and if he's back in time to replace Edwards if he's dealt, great. Some of the dreck they started like Abbott might be depth, too.
Starter, I/M/O, would be another place to look for help outside the organization. Knowing full well they will give as much of an opportunity to Cavalli, Gore, and Gray as they can, and that Corbin is a starter by default. I think there's still room for two starters so as to not concede any of the young guys a slot in the rotation, or Corbin if he needs to be moved to the pen. None of this assumes anything out of Strasburg, and assumes nothing out of Joe Ross. I think the latter is non-tendered.
So, one Corner OF/ 1B type position player and 1-2 starters. As for length of contract, 1-3 years.