Right now, the starters in April are:
ERod
Eovaldi
Houck
Pivetta
Mazza
I think Seabold gives them a little depth and we'll probably see Mata at some point this year. They will probably still sign another SP or two, so I'm not super concerned at the moment. Of the 55 SP free agents and QO's, only 8 have signed. I think they should re-sign Perez and Lester on one year deals. They will be able to throw a lot of innings and shouldn't break the bank.
My Opening Day rotation would be:
Lester (have him pitch home opener)
Eovaldi
Perez
Pivetta
Houck
ERod can ease his way back into the rotation and you can cycle Pivetta and Houck out once Sale is ready.