Don't let the diabetes and blood pressure thing scare you away from it. It's not impossible, it's just more difficult. Mainly, more trips to the doctor to get checked out and statements from him/her.
Quite frankly, if I where going to the trouble of obtaining a CDL, even if just to drive a school/church bus, I wouldn't fool with a Class C at all. It doesn't cost any more to go Class B, or for just a little more, a Class A.
You never know when that odd job might come up that your buddy needs someone to drive a dump truck for his construction company one summer.
The only added difficulty is finding a Class A or B vehicle. All you need for a Class B is a some sort of straight truck (dump truck, flatbed, etc.) that requires a CDL to take the test in. If you want a Class A, all you need is the same truck with a trailer.
But back to the medical thing, it's all dependent on how your ailments are being treated. If it's all under control, you shouldn't have any problems, other than some extra leg and paper work.
Anyway, check with SD, things change all the time, and the info I'm giving you is dated, I changed jobs several years ago and haven't been behind the wheel of a big truck since.