First boat, aluminum, pitting/oxidation and a hole HELP

Bought my first boat last year. 2000 Tracker, had a marine shop go over it, engine good. I asked them about the bubbling paint around the heads of some of the bolts in the transom, and they said thats a problem with aluminum boats, but shouldn't be a problem.
Fast forward to today, I find a hole about the size of a pencil. I have sanded, cleaned an jbwelded it. However, looking around, and especially underneath between the bunks I found significant pitting and am afraid of what is to come. What can I do? How much would it cost to have someone fix and would it be worth it? Can I tackle it myself? From what I've found so far, sand and clean then maybe marinetex followed by gluvit for the significant pitting and just gluvit for the oxidation after sanding then all followed by primer and paint. Is this the preferred method? Some other options?
Thanks in advance
Will try to get pics up later

Are the bunks pressure treated lumber?

My Gregor had a lot of pitting on the bottom of the hull when I bought it last year. I bought a bunch of paint stripping attachments for my drill and ground away hoping for the best. Luckily I didn't create any holes, but the pits were pretty bad. I primered and painted the hull. The previous owner said that his father used this boat in fresh water only, but it had been sitting outside for 20+ years.

Good luck.

I went through something very similar this summer with my boat. Is the pitting on the outside of the hull? Some pics would be very helpful.