Sorry if I do not understand the basics of forum search.

Does anyone know of a mod that basically 'completes' the main quest prior to new game start, so that the game that I play is even more free-form. I kind of like the idea of being able to go anywhere without having the main quest hanging over my head.

I'm not sure there are any that complete it for you, but there are many that have it so that the main quest never starts. I use Arthmoor's alternative start mod, works pretty well. If you don't want to do the main quest, just don't go to Kvatch.

There is an alternative start mod that disables the main quest. Your character starts in Leyawiin with only some basic gear.

Disabling the main quest doesn't help much for mods which may require you've completed it. Like Verona House.

There was a mod once that supposedly went through and set all the quests done as though you'd done them yourself, but I doubt very much that every last necessary detail was covered. Getting something that immense right would be a massive undertaking. Searching dialogue, triggers, quest stages, and everything else to make sure all the flags are properly set just doesn't sound like a lot of fun to me

There's one called mqsdone_zip which claims to accomplish this goal. I've tried it, but eventually ran into some anomalies which lead me to suspect it hasn't really covered all the issues Arthmoor alludes to.