#1 - Try to work the fenders while they are on the truck. This provides a stable work environment and you should be able to get to any dents to pound out from inside the wheel well. If the bottom corner is rusted out, as is typical on those fenders, it may have to be removed for that repair.

#2 - If the cab corner is "minimally" rusted you may be able to just cut a small patch instead of replacing the whole corner. Can't tell without pics. If you have the tools you can do this repair yourself. If not you can always rent a welder from Home Depot to do it with.

#3 - Without seeing a pic of the truck is hard to tell what to do on this one. If there is surface rust it must be removed and treated prior to any priming. If the pol paint is still there I would just sand it smooth and prime over it using an epoxy primer. The sandable high build primer should not be used as it will collect/absorb moisture over time and start the rust again. You might consider getting some Zero Rust in a quart and spraying the truck with that. It will last a long time, prevent further rust but will need to be scuffed and sanded prior to any future priming and painting.

Send some pics and we can see where you are starting from.