Really the buildings might be closer to the beach, but not excessively so. It's going to be a problem up and down the coast (With exception to Orlando, almost every major Florida City is coastal.). While Florida is considered the Flattest State in the Union, it's not the state with the lowest average height above sea level. That honor goes to Delaware, which has a mean height of 60 feet above Sea Level. Florida has a mean height of 100 feet above sea level and it's highest point is Britton Hill in Paxton Florida, which Peaks at 345 feet above Sea level. Judging by your map, most of the land east of I-95 will still be high and dry above Lake Okeechobee. If there are still Miami would likely have been mostly abandoned, though assuming that you can build large communities under the ocean, you should have the ability to construct large sea walls to prevent the flooding. Fort Lauderdale is probably now an island... if it hasn't been flooded.
That said, Florida is a massive state. It's the 8th largest by land area, and 3rd by population. What's more, it's got plenty of room for more people. Flordia's current population is extremely recent. For much of it's history, it was too hot and humid to be a desirable place to live (until the air conditioning made it bearable). What's more, with exception to Orlando, most of Florida's major population centers are coastal. Miami, for a major city, is a really small area comparatively. As you go further north, urban development west of I-95 (The eastern most Interstate and one quite close to the coast in Florida drops off), to the point that by the time you hit Melbourne (4 hours drive north from Miami, 1:30-1:45 East from Disney) there's almost no property development past 95. Driving North, your right side of the highway will have a lot of development and your left side is empty swamp and grassland.
Alligators would not be endangered. In fact, as of writing, alligators are listed by the IUCN Red List as Least Concern and were removed from the U.S. Fish and Wildlife's list of Endangered species in 1987. This is inspite of the fact that Alligators were hunted for their leather from the 1800s and 1900s in numbers that devastated the population. Critical changes include the fact that Alligators are actually farmable and the demand for gator leather has go down (it had a huge popularity spike in the 1890s). They're also not aggressive compared to the American Crocodile (You still don't want to approach one, but most people living in Gator country are not alarmed to see one up close... with Floridians being famous for their exceptionally calm reaction to a surprisingly close Alligator within their small back yard. Alligators are ambush predators and wait for their prey to approach them... so as long as you don't get close, a Gator won't run at you) and while gator attacks are on the rise, it's more because gator populations are rising, not because humans are encroaching in their territory. Alligators. In fact, Alligators can be found as far north as the Atlantic Coast as South Caroline and as far East along the Gulf Coast as Texas... There are also reports of breeding populations of Alligators in Oklahoma and Southwestern Tennessee. While they are more common around inland bodies of freshwater, they have been observed eating sharks and rays. Alligators might not be aggressive... but they are not picky eaters when they get food... or things they think could be food.
