According to Buzz Price's book Walt's Revolution, the Florida Project was initially called Project X. This was the
Disneyland East initiative.
It started with a proposal from NBC who was going to air the Wonderful World of Disney after the contract with ABC ran out. NBC wanted to get a theme park to go along with the new show just like ABC did - but withholding Disney's ability to buy back it's share (a mistake ABC had made). This theme park was to be built in New York City. Walt decided against New York because the park would only operate 120 days per year. He also said "that city is different. Its tourism is different." This was in 1959.
Also in 1959, Walt considered a four-way development project with Disney, RCA, NBC, and John McArthur. McArthur, an insurance man, owned 12,000 acres in Palm Beach, FL. This was the point at which the EPCOT acronym was created. RCA eventually backed out.
Disney then moved his attention to Ocala as the first choice and then Orlando. There were also studies performed on Washington D.C. during this time. Orlando was finally decided in late 1963 (after the World's Fair). Project Summer began in 1964 to aquire the 27,000 acres.
Buzz clearly states that Miami was never in contention like many people think.
I hope this clears things up.
Zach