At what point can a sleep apnea patient stop seeing sleep doc? Copays too high, in debt. Machine showing. 4 ahi for 30 days.

That's great! That's great that your ahi is down...Congratulations! but you need to keep seeing your md to make sure that you are not having any complications, and that any other health issues that may/may not be related are being managed as well. You should also see your dentist regularly to make sure you are not having any bite changes from your cpap. I know it's expensive, but it could save your life.
Depends. Sounds like you and your primary doc should discuss but usually once diagnosed and controlled regular visits are not needed. The sleep center usually maintaines accessories at no copayment and your insurance dictates the interval of replacements. Talk to your doctor. A phone call might suffice.