I've been busy and haven't posted or answered questions. Let me try to catch up:
@Bighead38 - The pictures may not be very good but the fireplace is on the second floor. When I lost the bathroom, the bar that was on that wall moved to where the bathroom was located. I needed to do something with the space and it was a bit cold last winter. The fireplace will let us heat up the mezzanine level locally in the winter and potentially allow us to use the space more often over the winter months. I plan to use the space to store cars and do light work like detail, oil changes, tire changes, brake changes, brake flushes - simple stuff. Maybe as I realize I have more space, I'll do more. I think I will still be limited by time not space...
@55cadillacking - Thanks!
@Bib Overalls, SiGmA_X, Redwolf947 - The added studs are for different reasons. On the main floor under the mezzanine, the studs are there to tie the x-brace and make it meet siesmic code. It may be that the drywall has to be there to protect the steel for fire code but I'm not 100% sure.
On top of the mezzanine, the studs are being added for three reasons. First is for the fireplace. It needed to be inset in the wall and decided I didn't really want to put it in the shared wall between units. I also thought visually it would look nicer put in its own stub wall with the stub wall painted a different color. Second, the rear wall where the bar cabinets are going to be hung have a big steel column that holds up the roof and big steel truss that runs parrallel to the ceiling that is also boxed out. I decided to put a little stub wall there that fills in the space so that the cabinets would not have to snake around the upper truss and column. The third is the currently free standing bar counter stub wall. The bar counter will have two levels with the first at the normal counter height on top of the cabinets and a second level at bar stool counter height. That second higher bar counter is tied to this short stub wall instead of the cabinets.