Sources intimately familiar with production tell TMZ, Florence was chosen because "it's young, walkable, fashionable, and beautiful in springtime" ... and, BTW, riddled with alcohol-guzzling clubgoers.

But we're told the cast ain't doing the city like your average tourists -- according to sources, they won't be living at a normal house ... or a normal hotel ... but our sources are mum on exactly where they will be staying.