Painting over Original Paint

[ItWillBeSlow]

I am currently working on a game plan to paint my truck. I will be starting with the firewall in order to get some mechanical tasks complete in the engine bay before working on the cab and doors/hood.

I plan to paint over the original paint in this area, using a single stage urethane from a high quality manufacturer that is TBD (recommendations?). Im going with the OE medium blue that the truck was built with.

The OE paint is in great shape on 97% of the firewall, with exception to some mild surface rust near the heater box, brake booster, electrical connection gasket, etc.

What is the proper way to remove this light rust prior to scuffing and shooting primer and paint? I also have some very mild areas where I scratched the paint to bare metal while chipping away at the original grommet sealant.

I plan to use this same method for my interior and dash as it is also in 97% "good shape". Truck will be a high quality driver, perfection is not necessary but I am doing my best as an average joe. The rest of the truck will be going to bare metal as it is not in the same condition.

Thanks in advance!