A team should probably have about 10 SPs ready to go for a full season. Might not need that many, but a team should be prepared if they do.
If ERod returns, they should have ERod, Perez, Eovaldi, and Pivetta ready on the MLB roster. Mata and Seabold in the minors. That's 6, and 7 if they think Ward is good to go. So maybe 3-4 SPs, at least two of whom will need an option year.
But maybe 5 if ERod just can't go, Ward isn't added to the 40-man, and maybe if someone is dealt...