Miami currently has no plans to supply LNG to cruise ships. The LNG bunkering at sea is still in infancy, so the year-round Miami ship will most likely be a Dream class. A second ship will also sail from Miami in the winter - most likely one of the classics or another Dream class.
PC will get two of the three new ships for year-round sailings. The third new ship will probably sail from a number of ports, incl. seasonally from PC. It may spend the summer in Europe - all of Barcelona, Hamburg, and Rotterdam have excellent LNG infrastructure.
The new agreements with the ports are for a minimum number of passenger movements - not sailings. In Miami, Disney is guaranteeing 360,000 movements. If it goes ahead with 4- and 5-day Dream class itineraries year round, it will move ~280,000 passengers annually with one ship. The second seasonal ship for three months will get you the remainder.