Have you thought about using 2x6 trusses and placing them farther apart. When I built my 40x60 building I did that and placed them 6 ft apart. Same load specs as 2x4 on 2 ft centers, but a lot cheaper overall cost. . We have had 17" snow loads with no problems. If you decide to put a ceiling up, you need to use metal as drywall won't work with 6 foot between trusses. You can always go 4' instead of 6 ft.
You also need to put some diagonal boards between some trusses for additional strength.
Personally I would forget the small block wall and just put concrete anchors in the floor, then spend the money to buy longer studs. Cheaper and just as good. Then make the walls slightly taller and put in a flat ceiling. Your design looks nice on paper, but a flat ceiling that's higher is more practical. If you insulate with blown in insulation, it will tend to gravitate towards the sides and be thin in the center. I put spray foam on the attic side of the ceiling to make an air tight membrane, sealing the metal rceiling panels to each other and the perimeter walls. Then I blew cheaper fiberglass/cellulose insulation on top of that. You can buy spray foam tanks and spray on eBay for about $600. Just need a thin layer.
Also, you don't appear to be leaving yourself much room for tool boxes and any storage around the lift. I would plan to install some used pallet racking along at least one wall. Then all the wasted space above your shoulders becomes storage space. You can even use one (or more) sections as a workbench by putting wood (and maybe steel) on one shelf. Really makes a nice workbench..... Utilize all that upper space and your shop becomes much more useful. (Note: I installed purlins between trusses to make them into pairs so they would sit on the walls without falling over. 40 ft was too big for me to handle without the crane anyway. Took crane about an hour to sit them in place. Then I filled in the open spaces with purlins.)
