If the Nats were to try to add another starting pitcher, then I would like to see them go after a high upside, riskier starter either coming back from injury or an off season than a safe average to slightly below average filler type. Garland is a bit better than that (average to slightly above), but at this point in his career, that is what Washburn's true talent is. Sheets, Bedard, Wang, are still out there.
The way I see the rotation setting up is that we will get close to 400 innings from Marquis and Lannan, and I'm pretty certain we can come up with viable 4th / 5th starters from among Detwiler, Stammen, Ballester, and Martin. I'd peg that combo for more than 350 innings. What we want is about another 180 innings or so out of our nominal 3d starter to get in the range of 930 innings. That would have been 10th in the NL last year, with 942 as league average. Right now, #3 would be Olsen, who, when healthy, is a 180+ inning pitcher, but is coming off an injury. If you can get comparable or better quality, and figure on getting a few months out of that risky signing, you can figure to fill in that 180+ innings with the Olsen / ? combo.
There will be some time when both are healthy, in which case you push one of the #4/ #5s back to the minors, and there will be some time when both will be down (or Lannan and / or Marquis may lose time), in which case you will probably have to have 3 of the Det/Mustache/Stammen/JD combo in the rotation, but, on balance, it should work in terms of innings. When you add in maybe 20 - 40 innings from either Strasburg or a recovered JZ at the end of the year, you will end up with 950 - 970 IP out of your starters, which would be top half of the league.
