You got a lot of GOOD stuff there!!
I've seen a lot worse start-ups!!
A lot of it will be just making patch panels and then cutting out the bad and welding in new metal. I did a lot of that on ol' Lockjaw!! A gentle touch with a MiG or TiG will be your best choice. Remember!! It's a RAT!!! Perfect is only what suits YOU!!
Here's some shots of different repairs I did myself! I DID order one lower panel for the right door. I had to cut it down and weld it in myself. The rest I had a local metal fab shop bend up pieces that I could do the final shaping myself. It was really inexpensive, but some of it was labor intensive.
You can see more if you check out my thread in Rat Rod Builds. Blackwater's Coupe's Gettin' Fat. There's a bunch of pics there too. A lot of other builds up there that you can glean information and see how others did it!!
Lots of great folks here!! If you wanna' know, don't hesitate ta' ask!!!