Just began receiving Medicare on top of Medicaid, have some questions

Okay so I am a disabled adult living in Arizona. I have been on medicaid for years, and now medicare has kicked in as well. I’m on SSI and SSDI combined, so qualify for both. But I’m lost on what all this means now and what my next steps are.

So to start with, should I stick with basic medicare or medicare advantage? And if I do basic should I get a medigap plan? Though I’m not sure if I could even get one because SSA forgot to add in my initial application for SSDI (they only processed SSI at first) so it took almost a year for them to fix that, and therefore my medicare “start date” is officially last February despite me only being able to access it since yesterday. And I heard there was some sort of six-month limit for medigap plans.

I can’t figure out if medicaid will cover any of the premiums or anything for traditional medicare and/or medigap and/or medicare advantage. And if I do basic medicare, that wouldn’t include prescriptions, right? Would I just be able to keep using medicaid for those?

I’m also lost because my pharmacy called me today and said they couldn’t fill by prescriptions because they don’t have the info for the medicare plan yet, though I haven’t even selected one at this point, yet it still showed in their system that I had one.

Finally, I have upcoming appointments with doctors through my medicaid plan. If they don’t take medicare, do I need to cancel and find new doctors? Or can I still see providers that only take my medicaid? And if they do take the medicare plan as well, do I need to contact them to update my insurance regardless?

Sorry I know this is a lot, but thank you in advance!