Novice question - after treating rust then what?

I check my car regularly for rust and I have found two small bits of rust, one on the edge of the door and one on the bottom edge of the boot lid.



I have found some rust treatment and intend to use it this weekend, but once I have (hopefully) removed it all, do I simply try and find a colour match for my car (x-power grey) and apply it?



Or should I be applying other products once the rust is removed?



Or should this job be better undertaken by a bodyworks centre?

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