Tips for bondo/block sanding/glazing compound . Amateur here

[89HatchbackLxi]

Grind / file any excess weld, without compromising the "holding" metal. Use Bondo sparingly with a flexible plastic spatula, so not to build it any higher than needed. It's sort of like drywall mud, but dries a lot faster. Don't worry about small cavities. They get filled later. Smooth first coat with rough grit (100) to shape. Apply 2nd coat bondo where needed and smoother grit (200). Look real close for low spots. Finish off with a can of self leveling paint will remove a lot of the scratches. Finish with 800 grit or finer before prime coat. Paint ready is 1200 - 1500 grit else scratches might show.

Good advice. Id add a couple things though:

Repaint the entire hood, don't attempt to blend it with your existing paint. It wont look right, and it won't last as long.

Also, once you're done grinding and have moved on to body filler/bondo always feel your surface for low spots when you're doing surface work. It's amazing how much you can feel the imperfections even when you can't see them. Use your palm to feel the surface, not your fingers. Don't ever put bondo ontop of an unsanded surface, or ontop of primer, doing so may not allow the bondo to properly adhere to the surface. And don't try to make it seemless using the bondo. It WILL break off eventually, maybe not at first, but it will later on. Bondo isn't meant to be used on its own, and it isn't very durable to begin with, so use of little of it as possible if you want good results.

As for the sanding, I'd personally not use any finer than 380 grit before putting on the primer. You gotta give the primer something to hold onto. The better it adheres, the longer it'll last. Besides, you'll be sanding the primer smooth on top anyways, so as long as you're using a decent sandable primer and you have a few layers on the car, you shouldn't have any issue with scratches coming through if you put it ontop of a 220-380 grit sanded surface. Once you have 2-3 layers of primer on, use a guide coat in addition to feeling the surface. Spray on additional coats of primer as needed until your surface is perfectly smooth.

Never make hard edges when spraying primer (aka don't put a solid coating of primer all the way up to the edge of your masking tape.). always feather your edges, this will prevent an edge from showing through later on.

Also, you only need to prime your repair areas. If you repaint the whole hood (as your should), only sand the rest of your hood down to the basecoat (so just get rid of the clearcoat). If you repair anything else on your hood, prime that area too. But always feather your edges so there aren't any hard edges.

Finish the repair bodywork and bodyfiller, then prime your repair areas, then sand and reprime, then use guidecoat and sand to tell you where you still need to prime( remember to always feel the surface whenever you are sanding throughout the repair process). From here, you need to reprime any areas where needed, then finalize your sanding with 600 grit. You can use 800 after you use 600 if you really feel the need to. Either way, you'll need to wetsand when using 600 or higher to avoid scratching unevenly while sanding. this is messy, but works very well.

Once everything is smooth and sanded, you'll apply the basecoat over the entire hood, about 3-4 medium wet coats (let them flash off -aka wait 5-10 mins for the reflectiveness to go away from the paint surface being wet). It doesn't need to fully dry unless your paint specificly says to let it fully dry in between coats. You may need to apply more coats if you can still see a different color where the repair is underneath. Then switch to clearcoat after however long your basecoat/clearcoat paint recommends, based on the type of paint and your work space temperature. Put 1-2 wet coats of the clear on your entire hood. Careful not to put TOO much on at once though, or you'll get runs in your clear.

Let dry, and enjoy the results of your hard work.

Oh, and in the meantime, lightly sand the surface layer of that exposed metal and put some temporary primer over it until you are ready to start your project. The last thing you need is rust forming on your exposed metal.