If you are going to restore from ground up, your expectations are too high for any garage. (At least that's my experience) how good a place depends on the mechanic, tinkerer, painter, and your scrutiny. Unless they are beemer fanboys, they won't fuss about every tiny bit of the car. Any worker would do his bit of work well. But making sure everything is put together nicely and neatly is your job.
I would suggest you to do it at your home. Those who work at your place have lower charges. If you don't have the time to get involved, choose a garage. Find someone who is a classic/beemer lover. You could expect honest work.
It's nerve wracking to get some of the workers do what you want. Like removing wires without cutting, prying trims without damaging, aligning stuff when fixing..... etc. I'm learning this the hard way May be it's only me and my OCD making things difficult.