If you're going to run tandems, you need to get 7 innings combined, preferably 8. Your bullpen will be short so you don't want them throwing 3-4 innings. You probably should drop pull to 1 and set PC at 55/60. At 15 pitches per inning, you're getting 4 from each guy except for the bad outing. Hopefully you get 3 from a guy in that case.
If you don't have 6 guys who can handle 60 pitches every 4th game, you're probably not tandem-ready. If you're forced to go 4 tandems in order to make it happen, you need one of those 70 Dur/40 Stm pitchers in the pen. Otherwise, you're going to end up carrying 13-14 pitchers and that's inefficient.