Wow! You made an impression on several fronts...tree.....Mustang...
At least you weren't hurt, huh? So, you dad made you work for it by building a garage. That's good. Now, you know something about how to do that and it can come in handy to help you find a job that may be helpful to you as you upgrade/customize your truck. That's good, too.
The nice thing about these trucks is that there's still a lot of decent parts out there that are basically affordable. As for your wants on the grille, why not change to the later (94-98) GMC grille and then the clear markers/corners you want will be readily available? You'll also need to change the valance between the grille and bumper to make the grille fit. You won't need to change headlights from the quads you now have which isn't a bad thing because the glass lamp assy's won't turn yellow unless you have low voltage going to them. You could keep those and add the clear parking lenses and then the clear corners. A smooth front bumper (no rubber/no holes for license plate) would clean up the front end. Shaving the tailgate shouldn't be too hard. Mar-K in Oklahoma City has a kit to relocate the tailgate handle to the inside of the tailgate, that includes the patch to cover the hole. There stock handle goes on the inside of the tailgate so parts are not an issue if the handle goes bad.....stock GM still will work.
But welcome to our forum and we're waiting to see how your truck goes. Keep posting pix.