In addition to Brian's post which is loaded with great information
, put the filler on like it's the only coat it needs because you are working within the product's ability as stated on the technical data sheet you read.
Secondly, you'd be better off to fill one area with a mix or two of filler, then sand it and reapply as required until you're happy with the result. The reason is twofold 1) you have less chance of creating a bunch of repair work due to your inexperience and 2) filler can get harder to sand the longer it's left. It's best to only apply filler that you're sure you can sand same day. It cures pretty fast (about 20 minutes) so planning ahead to sand shouldn't be a problem.
Keep in mind you are going to use a glaze putty (2 part!) when you're done filling so you don't need to get it perfect with the filler. Get the filler to 95% perfect, glaze to 99% perfect then the high build will take you to 100%.
Post pictures of your work...we all like pictures