I don't get hung up on SP's beyond my #1 and #2.
What I typically do is give them all 3 to 4 starts to get a little bit of a body of work under their belt. After the third of fourth start of the season, juggle the rotation based on the performance of your 3/4/5. Whoever bubbles to the top becomes #3, then #4, then #5.
This can and most likely will change (multiple times) as the season progresses based on performance.