I'm not sure about what YHM does for installing a brake. Do they mean they will weld it in place for you and everything? Or just thread it on and straighten it? If they'll weld it, that might be worth it, but if its just to thread it on, I'd save yourself the shipping cost and do that yourself.
If you do want to ship it, you would probably need to put on the barrel nut and gas block at the very least. Check and see, maybe you will be lucky and the barrel nut will fit over the break. I've used some breaks that were small enough diameter that the nut could clear it.
I would then make sure that your free float tube will fit over the muzzle break, otherwise you better thread that on too before the break is installed. Oh, and you would need to have the gas tube installed before that too.
If your free float tube fits over the break, I would probably wait to do the gas tube, so it doesn't get damaged. You can lightly install the gas block without loctite. Then when you get it back from YHM, loosen it up, push it down the barrel a few inches, and then install the gas tube into it and reposition the gas block to permanently install it in place. Then put on your FF tube over everything and you'll be good to go.
Not to be overly cautious, but you may want to rethink all this. If I were you, I would take your barrel, mount it to your upper receiver and torque it down. Install the gas tube and block. Then go to the range and test fire the gun for proper operation. You can test fire without the FF tube, and without the muzzle break. This way, if there is anything wrong with any of the parts, you can diagnose and fix it before its too late. Once the muzzle break is welded on, it is going to be very difficult.
I realize that this all seems incredibly unlikely, but I've had two builds (built with quality parts) that I had to take apart and replace faulty components. One was a bad gas tube and the other was an undersized gas port in the barrel. If the muzzle break was already welded, it could've been a nightmare.
One thing...IANAL but note that you are breaking some laws when you go to the range to test fire it without the muzzle break welded on. So just keep that in mind and act accordingly.