OP is asking about sole practice. In such a case, there's no minimum income, and it cannot be related to what someone might pay you as an associate. You earn whatever you earn, which could potentially be very little, yes. Doesn't have to be, but it's a real concern not to be dismissed lightly.
I'll try to post something intelligent soon. In the meanwhile, OP, start by reviewing this topic. It's going to answer at least some of your questions.