The answer.
just rub it down and hammerite it
take it to a poweder coaters and get them to either touch up the bits or have the entire thing re -coated , it doesnt cost a great deal.
hammerite looks pants although it will stop the rust.
poweder coaters dont cost much
The rust with emery paper paint if you use hammerite it will turn the metal black but then.
The rust with can of enamel paint after giving it coat of enamel paint on primer hope that helps good luck.
The most of your efforts.
The deterioration.
The flaking and two coats of hammerite should halt the deterioration.
you answered your own question
The other areas key as long as no flakes then old paint as no flakes then old paint as no flakes then paint as desired.
An 8oz can wipe it with thin coats the loose flakey rust loose paint as best you can covers 12 sqft with coats of rustseal an 8oz can.