How hard would it be, once the construction set it released, to remove all of the quests in the game (and have an alternate start location, of course)? I tried it in Oblivion, but it was pretty impossible for me.

Also, I'm pretty sure I saw an alternate start location mod on the Skyrim Nexus, but I can't find it anymore. Has anyone seen one recently?

Just download one of the save game files of chars on level 1, type showracemenu in console and you have your alternative start location. There is no constructor yet so this is the best we can do.