I'm looking to have a copy of Lightroom installed on 3 different computers (One desktop at home, a decently powerful laptop and a Surface Pro tablet for when I'm traveling light). I know I'm allowed (and am using) 2 copies with my Creative Cloud subscription; if I purchase a retail copy of Lightroom by itself will I be able to associate it with my existing Adobe ID and install on 3 machines?
If you have CC and a retail version of the standalone version of Lightroom, you're fine installing on 3 computers. There's no need to associate it with your existing Adobe ID, everything will work if you don't. You should register the retail version with Adobe.