Your local auto paint store will have tech sheets for each product. But that won't help you with technique.
Most body working books are also very outdated. Youtube can be a good place to go to see what processes people are doing these days, and to witness some techniques.
Tim is correct- bare metal, then epoxy, then filler, then primer(s), then sealer, then paint - seems to be the favored process these days.
If you have to drill holes through the metal to hold the filler, then you need to get out your hammer and do some more panel straightening. Don't use thinner or acetone to prep bare metal- there are products specifically designed for this. Bare metal is typically sanded with a DA sander with correct grit paper to prep and provide a tooth for primer/filler to bond properly. Or sand blasting.
That said, if you're not looking to invest a lot of time learning the process, and/or investing in the tools and materials (which are kinda pricey), there must be a few quick and dirty methods to deal with it that won't cause too many people to shudder in horror....or have it fall apart in a few months...but I just don't know what those methods are. Perhaps someone here will have some easier ideas.
I believe that for most body fillers, 1/4" thick is the absolute limit. IMO, that is crazy thick.
Whatever you do, be sure to get as much info as you can from the paint store reps- some products are not compatible, such as epoxy products and anything with acid in it, such as etch-primers. And by "not compatible", I mean that it will de-bond and turn into to freaking mess (sometimes in very short order).
