I'd go with 13 pitchers until April 15 or 16, when we are 4-5 games into a long stretch or no days off and after we have 2 days off in the first 9 days of the season.
We might go longer, depending on how deep we had to go into the pen over the first 2 weeks of the season. I can't see Brice and Brewer being overused by the 14th or 15th game of the season. Chances are even having just one of the two won't see overuse.
I never thought I'd hear myself says this, but I want Chavis on the opening day roster. (I also think we need Arroyo or Arauz, too.) IMO, the only argument against Chavis is Duran not Brewer, but I guess it is what it is.
We have a few guys that can go long innings in relief, in case a starter gets booted early a few times in the first 2 weeks. They can go long (3-4 IP) maybe 3-4 times in the first 14 days, so the one inning RP'ers should not be overused. If things fall apart, early, then make a roster move once you look to short-handed in the next game. These guys at the alternative site should be readily available and on-hand in less than 24 hours.