Gonna start playing Skyrim again now that i bought Dawnguard and Hearthfire, but i need to know if the vampire invasions continue after the main quest is finished (i already know they start as soon as DG is installed). I'm planning on creating a new character just for some vampire killing action, but with my old characters i really want to avoid getting hassled by vampires every now and then.

Don't think so.

Nice. Thanks for the answer!