Hi, Ana
You should be begin by reading here > https://www.airbnb.com/help/article/890/miami-beach--fl. There are useful links about zoning and Airbnb requirements in Miami Beach. Your property or unit has to be in a specific zone or you can be fined by the city.
Yes, Ft. Lauderdale is cheaper to buy. There are then different zoning codes for Broward County. You could also hire a property management company, but this can be expensive (at least several hundred a month). You'd have to make volume bookings (rather than seasonal) to off-set the cost. I offer to live on-site and help manage your bookings in addition to cleaning, in exchange for free or reduced rent.
I was a Superhost at my old place near UC Berkeley back home. I posted here to find a new place in a more walkable area of Miami in exchange for helping support the owner with the Airbnb platform and hosting. I helped a former guest set-up her own Airbnb in Seattle - from how it functions, messaging, calendaring, pricing, and posting photos of her space.
Let me know if you want to talk further.
My thanks!
Lisa