I'm new to the Fold 3. Had Notes before from the 4 until the 10+ that I traded in for my Fold 3. I've had it for a week and love it so far. As to cases, I tried the S-pen case but wasn't impressed. As Maxishighroller said the flap leaves a lot to be desired and I don't think the case offers much in the way of protection. It reminds me of the flap case I had for my Note 8. Dropped the phone once and it popped right out of the case and cracked the corner of the screen. In addition, the slot for the S-pen storage creates a big bump so you can't lay the phone flat when it's open any more. Think of it as though you laid a book down on a pencil.
I returned the case and went with the Samsung Silicone case. It offers a little more protection and the phone won't be popping out of it. While I originally would have preferred a clear case, I decided it was a moot point as I'm hard pressed to tell that my Phantom Green phone isn't Black anyway.
Finally with regards to the S-pen as I mentioned I've been a lover of the Note series for a long time. However, I was extremely disappointed to find one, there was no internal storage for the S-pen and two you can't use it on the cover screen only the inner screen. Therefore, I've opted not to bother with the S-pen. While I miss it, the larger screen allows me to use my large hands on the phone comfortably so it's not a major inconvenience. In addition, I was disappointed as to how much the S-pen left tiny scratches on my Note 10+ screen and didn't want to chance the same happening with the fold.