My new one is 40x60, I can see it filling fast. Also adding cement in key spots for adding mezzanine and a lift. It is drive through, but not for everything.
10ft walls seem low, look at 12-14. Im going 16 and it gives a 21 center height. You might be OK if you need a steeper pitch, I only have a 4/12.
I like heated floors, but not doing it to the shop, just the living space. If you get good winters, you will be happy. I only deal with 2 cold months and just below freezing.
I am keeping my container for storage, may even get another with a cover to keep the tractors out of the weather.