OSTA alone would require a SERM.
S4 why? and Cardarine is GW 501516 which is not a SARM it's a PPAR-AR
I'm assuming from the Osta, and GW you are on a cut, but honestly there are products out there that would save you money and the risk. GW has issues with cancer potentiality, and is for endurance, not fat loss. Ostarine alone could be on a cut (Muscle Retention) during a deficit.
You can cut and require no PCT or SARM
If you run a deficit, proper nutrients, and some key supplementation over a longer period you would achieve longer lasting better results without affecting your HPTA Axis.
You've got some research to do.
* Just saw above post response to OP. This should be in the Anabolics Section.