I'm currently building a 1200sqft workshop, not a hangar, but here's what I've done.
I did a monopour of 4500psi concrete with 2' deep footers. 6" thick slab with 1/2" rebar, 16" OC. I have some heavy machinery, may get a larger VMC in the future, and may occasionally have a forklift on the slab, so I wanted real rebar. This might be overkill for "just a hangar", but you really only get one shot to pour the slab and the labor costs more than the materials (by a factor of about 3:1 I found, although my area has high contractor prices).
I'm planning on epoxy coating, 100% solids epoxy at about 10mils dft (I already have the material on hand and am planning to coat it this weekend). I had the contractor hand trowel the slab, then put a very faint brush finish on. No sealer. I will acid etch the slab tonight in preparation for the coating. I've ground slabs in the past for coating and it is no fun, so if you're going to coat plan for it right from the start.
I had the footers insulated vertically on the outside of the foundation (and 32" up the exterior walls with 2" EPS as there is an 18" stem wall along half the building). The slab is insulated 4' in from the edges underneath the concrete, but not the entire slab. 2" thick EPS is expensive and if you do the math the added insulation may never pay for itself, depending upon your climate. Most of your heat loss is around the edges anyway. The insulation and concrete was placed upon 4" of compacted base course. I had a 6mil PE vapor barrier placed on top of the base course and insulation. I was pretty cautious to keep it continuous and unpunctured, however the contractors put the rebar on chairs (as required by the city) and the chairs seemed to puncture the vapor barrier during the pour. They pumped the concrete in and the weight of the hose pushed the rebar and chairs right down. I honestly think the chairs were totally pointless and did more harm than good. I live in a very dry climate (northern NM), so I'm not too concerned, but if I were to do it again I might pay extra to have it pumped in with a crane. They might do that anyway for a building as big as you're building.
I live in a very mild climate, but its pretty cheap to put the in-floor piping in for radiant heat, even if you don't put a boiler in right away. I didn't bother, as a 18,000BTU minisplit will be more than adequate to heat/cool my space.
Zach