So I consulted with my engineers last night at the NHRHTA Photo Archive. The challenge being how to support the upper deck. So Dick suggested I place the legs at the same location as those supporting the lower deck, and use an angled support to support the front. The deck will be attached to the wall, so it should have plenty of support that way.
So the easy part was the legs, but I can put up temporary cleats to add the deck. Here's a picture of the legs with 1x2s where the upper deck will be. One of the issues I had with the lower deck was getting it leveled since the legs are on the carpet. So I made them long as Chris suggested and I'll cut them to length after the weight of the deck helps them settle.
I'm hoping to make some progress on the deck tomorrow. I'm going to see if I can get some 12' 1x2s and 1x3s so I can make the main section in two parts.
Here's a picture from today's work: