I only regret not building a larger shop...or two. And an extra (separate?) space for boat, cars, forklift (which I don't have), etc.
6-car garage space is just too small for my junk. Having concrete driveway vs. asphalt would be nice too, but this is not a major problem.
Obviously, think about major stuff: good insulation, walls that you can use to attach stuff to (I like OSB), a lot of light, many outlets everywhere (both 2-gang single and 3-phase), compressed air lines with multiple drops, separate compartment for air compressor and RPC to get rid of sound, space for welding gas cylinders, exhaust in the welding area, HVAC (radiant heat tubes may work well with high ceiling- so gas line of a suitable capacity will be needed). You already installed Internet, so security should be thought over too. Consider dehumidifying options if you don't like rust on your tools, machinery and metal stock (you are in Midwest, I suspect): good insulation alone would help immensely, but I prefer additional dehumidifying which may be challenging for such a large shop with large doors. I assume you have good attic ventilation.
I don't know what you're going to do there, and how much time you are going to spend in. So I base my suggestions on my experience with my serious hobby metalwork shop with very basic woodwork.
One thing that I don't regret is that I didn't do epoxy floor. Sure it looks nice. But what a slippery nightmare it would be, esp. with oil leaks! And metal chunks dropping on the floor won't be too good for epoxy either. I learned this after having epoxy floors installed in two basement rooms: ceramic studio and utility. The first time I stepped in, I could hardly walk because it was extremely slippery despite some grit and floor being dry. Then I asked the guy who did it to add more grit. I can walk there now, but mopping the floor is a headache because the grit catches the mop.