Thanks to all for the thoughtful responses.
Paulharvey - I think I've decided on 26 gauge. I did contact a geotechnical engineer and am waiting on a quote. Hopefully they can advise on the concrete thickness as well as any reinforcement. The only finished walls will be in the workshop/heated areas. Will likely do some kind of wood sheet material I've heard about in the shop and perhaps drywall in the hobby area. I'm still exploring what sort of insulation might be best for the unheated versus heated areas. I'll be running power, water and sewer and will need to think about setup before pouring the foundation.
Height and doors -- Still internally debating about door/ceiling height. 10' high door at a minimum -- but still thinking about how much higher, if any to go. For the two outer buildings I was looking at 20' wide doors and a 12' wide door for the drive through -- might consider the 16' as wmonroe is suggesting.
Boggen - Thanks for the advice on shape. I think I initially went with the T shape in part due to curb appeal. My wife isn't crazy about the barn being larger than the house and is worried it will be the center of attention of the property. I figured the T shape might appeal to her a bit more in this area rather than a straight monolithic rectangle. Also, there is some slope front to back, with more slope the further back you go, so the drive through doesn't work that well if I had to pull straight in from the front and exit the back, as the land would need to be built up quite a bit in the back to accommodate the driveway out the back. The drive through in the front from left to right gives me a level area that would take advantage of an already present driveway area. But I take your point on functionality, so will need to consider and see if I can achieve the curb appeal factor and better functionality at the same time.
Bspeedy - Yes, Pelzer is right around the corner from Easley. I'll definitely consider the rectangle setup as suggested. But as mentioned, just need to consider the appearance and how the drive through might work with the slope.
Kubota6040guy - I was kind of relying on a builder friend and the metal building guy to advise on the trusses and wood/steel materials, but I'll ask now that you bring it up.