You Sir are an artist!
You've inspired me to do the body and paint on my 64 D100.
So far I've purchased a mig welder and a board sander. (Already have a compressor).
Is there anything else I'm really going to need?
I started under eldubb440's tutelage a couple of years ago and found his advice and pictures invaluable; so THAT'S one thing I suggest you need! Here are things that I've found useful that I wish I had from the beginning:
1. Angle grinders. Get a couple so you don't have to switch the cutting wheel to the grind wheel; have a grinder and a cutter. Get the lighter/less amperage ones as the heavier ones wear you out with the extra weight. I've got a couple of 4.5" 4.3 amp grinders that are a delight to hold. I bought mine at Harbor Frieght for $15 each.
2. A nice hammer/dolly set for metal work. There are so many dings and dents that can be tapped out.
3. Lights. I bought a number of the rechargeable 500 lumen LED wands with magnetic bottoms that stick anywhere.
4. Face shield (if you're doing a lot of cutting like I am). I have safety glasses, but crap flies up into my face and the face shield works best. (Note: I bought my face shield after going to the optometrist to pull a small metal piece from my eye.)
5. Don't laugh but I wear metal mesh gloves under my thin leather work gloves when cutting or grinding. I've hacked into my hands too many times and, while the metal mesh gloves won't prevent a full-on cutoff wheel, they do give you that split second to get your hand out of there.
6. An extra bottle of welding gas. Same reason as you have an extra propane tank for your barbecue grill.
7. Here are more:
Okay, in rereading my suggestions, I guess most are based on my newbie's hypocratic oath: First, do no harm
Regarding welding for first time welders:
1. Practice your welding on places that no one will see: wheel wells, trunk, floors, etc. When I look at my first welds I wonder what I was drinking....
2. Yes, heat warp is a thing. Let it cool. (Newbies aren't known for their patience.)
3. Watch videos by Fitzee's Fabrications. The guy's a whiz with welding and fabrication.
Terry