Welcome aboard!!
Great boat.
I'm not clear if those thru-hulls are chrome plated or not, stainless or bronze. Pitting would lead me to believe chrome plated bronze. In which case there's nothing you can do other than replace them to correct the pitting. Saltwater will do that to them. They'r probably structuraly sound, just cosmetically affected. If they are polished stainless then a good metal polish would help a lot.
I've been using metal protectant on everything that's stainless or chrome on mine to try and keep that from happening. That and keeping it hosed off after every trip.
I would try some Flitz or similar, metal polish, just to clean them up and probably make them look better. Just be happy they're not plastic or you would have to replace them to be safe.