Looks like it’s an assembled car right? If so media blasting isn’t the best approach.
Get a couple of Clean and Strip disks for your angle grinder, a good quality wire wheel for your drill or die grinder and a phosphoric acid based rust remover like PPG DX520 or evapo-rust.
Deal to the bulk of the problem with the strip disks first, and feather out the old paint and filler until you find clean metal and well adhered coatings. The strip disk won’t quite get into all of the crevices and pits so hit these with the wire wheel before treating the metal with rust remover - be sure to mask off feather edge so the chemicals don’t seep into or under the surrounding paint and filler.
While your rubbing on the rust remover with an old scotch rite pad or steel wool look real close for black flecks (rust reacting with the acid) if you spot any leave the acid for a while and hit the flecks with the wire wheel again. Rinse and repeat until no more black spots show up.
You’ll probably find some of those pits turn into pin holes, and in this instance drilling them out, priming the area with weld through primer and welding in a plate like 75maro suggested is a really good approach.