I'd say the easiest way to turn your non-GFCI light circuit into a GFCI circuit would be to swap out the existing circuit breaker in the panel box that serves the existing light for a GFCI breaker. The breaker would then provide GFCI protection for everything on the circuit. When rooms are wired, often times the power comes into the room and goes into an outlet box, then runs around the room going from outlet to outlet. From the last outlet wires are run to the light switch and then the wire continues to the light fixtures. If you have a GFCI outlet in your bathroom that is wired BEFORE your light switch, then it's possible the light can be GFCI protected by that GFCI outlet. Not sure on that though, the wires would have to be traced by someone who knows what they're doing. Regardless...yes, you can replace your existing light with a light/fan combo. The locatin of the light makes it easy, for when you remove the existing light you'll be able to locate the ceiling joists through the hole where the light was. Just read the fan installation instructions before you go cutting into the tile, so you get proper clearances from the adjacent joists, etc. The easiest way to cut through the tile would be with a diamond blade mounted on an angle grinder.

A lot of times the walls can be renewed with a buffing wheel and automotive polishing compounds. Just take it easy if there is a gel coat on the surface, you don't want to "burn" through that. The floor can be difficult. Textured and slip-resistant areas can hold discoloration. You can try the compounds on the floor too, but it can be a little different with any texture on the floor. So I have no sure solutions for the entire surround, but thought I'd post anyway since no one else has replied.

Is it chipped down to the metal? I would definitely not get it refinished, but I would see if you could find some way to at least patch or clear-coat the spots to prevent future water damage. What color is it? We have an original porcelain tub (1928) and when we re-did our bathroom I thought long and hard about refinishing it. I ultimately decided to keep in original condition with it's beauty marks (a few light pits, some tiny black spots) and see how many more years it can go. Anyway, I learned a lot about shining up a tub, and so much of it is tools/techniques/products they use for car body restoration. This article from SF Gate explains how to actually repair a chip yourself.

I bought an AMERICH WRIGHT base level acrylic tub for $1,000 from a bath and kitchen store in 2017 and it is a piece of plastic. After two years It was stained, difficult to clean and never feels entirely clean, the caulk around the tub has needed replacement several times, and the Americh label partly wore off almost immediately. I never use any abrasive cleaning products (all organic). When I contacted the manufacturer they pointed out that I the care instructions said I was supposed to WAX my tub with high-quality carnauba paste type wax. Wax my tub? They also referred me to a very expensive tub cosmetic repair company. Unfortunately I removed an old enamel tub instead of refinishing it. Number 1 worst decision in my remodel after seeking lots of advice. I dream of ripping this one out and replacing it with an enamel tub. Taking a bath in an acrylic tub feels cheap even though it wasn't..