I think starters like to be in the rhythm of starting every 5 days early on.As the season grinds on, that extra day can give them a needed break or even skip a turn in the rotation if necessary.I'll stick with the prediction that we break with 4 starters and an extra body in the bullpen as we don't tend to stretch out starters early.I think they only need a 5th starter on the 11th and the 24th.They can do that by sending down the extra bullpen body or by putting someone on the 15 day DL and bringing up a starter for that period starting on the 11th.Of course all this assumes (dangerously) that Erv will be ready in early May.
Assuming 4 starters in regular rotation, we'd need a 5th starter on April 11, 24, 29, and May 4.Basically "skipped" twice in that span, the first week and the third week (around the Puerto Rico trip).
Depending on how they did it, they could skip them on their next off day May 9th too, but you would need them by May 14th again.
The DL is only 10 days now, so that helps, but I don't see them pushing Berrios, Mejia, etc. Early last season they were skipping the 5th guy a bit (Mejia?) but the other 4 spots were veterans (Ervin, Santiago, Hughes, and Gibson).