Sport pilot flight rules limitations

I've read Part 61. Its more than a little confusing. I understand the
limitations of a sport pilot flying under a "driver's license" medical.
That part is pretty clear. I currently hold an "old" commercial
license with an instrument rating and have quite a few hours. I don't
hold a current medical, but would probably qualify after an appeal
(there might be a couple of "disqualifying" conditions for which I am
being successfully treated). My health is otherwise very good.

Am I playing the lottery by thinking that I can get a medical?

But lets assume that I don't care to go after a 3rd or 2nd class medical
and that I hold a commercial ticket (CASEMELI). I have a diver's
license with no restrictions.

What are the limitations for flying a light sport airplane? Strictly
61.303 and 61.315 conditions only or are there other things I can do?
What about a 4-place fixed gear single engine (with or without cs prop)
airplane? Can I carry passengers?

Lotsa questions. The answers will help me set my expectations for a
return to flying and also to help in creating a list of possible kit planes.

Thanks in advance for the comments.