Congrats on the purchase. As mentioned above, don’t do the spacers to level the front end. If looking for a higher stance, search for a quality lift and go as low as you can to get the stance you want. Granted, a leveling kit would be cheaper, but the ride quality of GOOD lift kits can exceed the stock ride depending upon the setup. I am speaking from my experience with GM’s HD pickups. 2 two trucks I’ve had I put 4” lift kits on, one cognito and the other was a tuff country. Both had the torsion key bolt removed so they were essentially a glorified leveling kit, but the front end geometry was perfect, albeit a SLIGHT negative angle on the CV axles. Both trucks rode great. Others I’ve owned have been cranked slightly, but still in the “green” zone geometry wise. I know the HDs are totally different beasts and in a long winded post I am basically saying, get a lift.
On on the seat covers, I really do like my cover king seat cover in the back of my 18. Had cover king covers in my 04 too and were great as well. Fit well and looked awesome.