Wow, three updates in three days!
So I picked up some 12' 2x3s to make the main deck in two pieces. It went pretty quick actually, and they're up. With the legs already in place, I just put three clamps up and rested the deck on those while I attached it to the wall. I started with a stud about a third from the end, and just made sure that the top of the deck was at the level line. That way I could use that point as a pivot and screw into a stud at the other end of the deck. Once those two were attached, I made sure it was level and attached it to the legs. That was it. It was simple to go back and attach it to each stud from there.
Here's a picture before I completed the angled supports on the last two legs. I also hadn't cut the legs to length yet.
I'm hoping to have some time tomorrow to continue around the walls. I'd really like to cut the OSB for the decking itself, but I'll do the same thing I did for the staging and start with the corner pieces first. So I'll at least need to build the side wall decking for that, and I think I need to pick up a little more lumber...