Re: Aluminum Hull. First timer.
I can't help much with the rest of your questions, but I do know that most (all?) bottom paint manufacturers specify an expected life of their products, and how best to apply them & maintain them. Not knowing which paint is on your boat, makes it difficult to say how best to remove it or prep it for additional paint. I think some bottom paints recommend an associated primer...
I am NOT recommending this particular paint, or it's maker, but iboats sells bottom paint:
Pettit ViViD Bright Color Ablative Hard Speed Antifouling Paint - iboats
This ^^^ particular paint's info @ iboats gives LOTS of info, but to answer your other questions you may need to spend a great deal of time reading & researching which bottom paint best suits you, you're mooring & usage situations, and which of the many application methods (& paint type) is going to work best for you. Even if you don't read it all, scan thru the Pettit's info.
Saltwater & aluminum are not the best combination, make sure your zincs are in GREAT shape, and that you are not grounding your electrical system to the boat. Marina's also often have an electrical bleed into the water around the docks, so doing everything you can to protect the aluminum hull is important...