I think limiting the number of innings too much is equally harmful. This is fantasy baseball after all and some odd scenarios are possible. What happens if a team has its 5 rotation starters pitching twice in the same week? That team would be screwed because the following two weeks they would have only 5 starts a piece and won't even be able to capitalize the one week were they would have the advantage.
65 is probably way too small. 75 or 80 sound more reasonable. 8 starts at 7 innings a pop is 56. Plus some 20 innings in relief leads to 76 IP.