I think most schools have a minimum of 2, but prefer 3 LORs from professors and then the last one from a dentist. I'd look at the schools you're applying to and try and figure out the best combo of letters. Also I'd ask ASAP if you haven't already because you want to give your writers adequate time (like 2mo), and the later you ask, the later they write and send it, and the later your app is marked complete.
Varies by school, and with COVID, no one really knows how this cycle will go. At minimum, though, AADSAS needs to verify your transcript and calculate your GPAs, so it can be 2-3 weeks or even sometimes 4-6 weeks after submission before schools will ever receive your app.