That’s a pretty standard associate starting salary if you’re not on the coasts (meaning coastal metros will often be lower). Partners will generally eat what they kill, so what they make comes down to how busy they can/want to be. So yes, it comes down to patients per day for the most part, but there is usually some profit sharing agreement as well. I agree with the above that $500k as a partner would be part-time.
You need ~100k people to support one retina doc. If the catchment area for each practice is strong enough, competition shouldn’t be a problem as long as there are established referral patterns. If you don’t have a retiring or leaving doc ready to give you immediate volume (assuming your license and insurance credentialing are done), you will have to be patient as your practice builds.
Retina only versus multi-specialty is nuanced, but I prefer strictly retina. You have a built in referral system with the MS, but I don’t think I’ve ever heard of one in that kind of location that could support 4 retina folks. Also, comprehensive practices tend to have higher overhead, so you wind up subsidizing the non retina docs. It’s possible to balance that with ASC funds and some other bits, but you said no on that. Call can also be a little weird, including a higher likelihood of hospital coverage.