I sent this in a message to someone a while ago:
Aluminum is amazing but not painted; painted aluminum is fine until the coating is breached, then you get runaway corrosion under the paint, a bunch of white powder and the metal is disintegrating. Paint over a seam and the boat flexes in a stiff sea and the coating is breached. Even attaching something to aluminum, with the salt air, the attachment acts like a coating (keeping oxygen from contacting the metal) and it will corrode too.
There are only two choices: rigourously chase the cracks, remove the coating, sand away all the corrosion and repaint. Or get all the paint off. Aluminum, uncoated, turns a gloomy grey colour that many owners want to "fix" but if you polish, blast or use chemicals to remove the top grey coat, it will immediately turn grey again. It's that grey coating that protects the metal.
If you use fasteners, aluminum nuts and bolts (I have some) are just not good enough structurally so you'll end up using stainless steel. Use 316 anywhere outside and coat the bolt with neverseize (there is another product that protects from corrosion but the name escapes me) otherwise it will make a corroded mess and the bolt may permanently gall.
Insulate all aluminum that appears in the inside of the boat as it will collect condensation and soak the interior. For example, if you mount something through the finished ceiling and don't insulate the fastener, it will drip like a tap. I had a hatch that was lined with carpet. I thought it was awful and I pulled it out. When I returned the next day, my bed was soaked as the condensation had dripped on the bunk.
Wet aluminum decks are lethally slippery in bare feet. Al decks get very hot, bare feet will burn.
Al water tanks are hard to service, you should NEVER use chlorine in them.
You need to be very careful of the anodes, you will need more of them than a glass boat and they have to be welded on. I buy aluminum strap/aluminum anodes, they last about 30% longer than zinc and are still cheaper. I have 18 and 2 shaft anodes on my boat.
You should have an isolation transformer for your shore power so you can't put stray current in the water and you are less likely to electrocute someone.
Bottom paint: unless you have an epoxy barrier coat, no copper!
I love the aluminum on my boat but it will never have a "yacht" finish. I'm good with that.
There are other things like foamed bilges...