Before you start priming, look for any structural cracks. Fill in any holes and cracks with an underwater pool patching. The type of pool patching will depend on the style of pool you have. If you see any large cracks, it’s best to call in a contractor to ensure no significant issues are under the surface.
This question will be answered with a big "it all depends". Your pool's life expectancy can be extended if the water quality is maintained and properly cared for. Homeowners and commercial property owners tend to keep their pools surfaces pristine for longer periods of time than they need. When your plaster starts to peel, flake, crack, or become rough, it's time to resurface.
A fiberglass coating is something I would not apply to my skin. Methyl Ethyl Ketone is the catalyst for isophthalic compounds - no Bueno An epoxy is safe to roll on. Be aware of the fumes and gases that can be inhaled when you apply coatings in areas not ventilated.