Went through this recently. So, I used 5052 in a .040 thickness. It was a plain mill finish, which gives it that "brushed" look. I'm not sure what the "clear anodized" finished you mentioned looks like. I could have used a thinner alloy, but the .040 is stiff enough to eliminate any "ripples" that you might get with a lighter thickness, so the end result is more forgiving.
If I had it to do over, I think I would have just cleaned the original skins and then painted them. Some things to think about include:
Material volume: For my 21' Globetrotter, I used an astonishing 10 sheets of aluminum 4' x 12'. They cost about $50/sheet from a local supplier. The issue is that with the milled finish, you get a lengthwise grain pattern. You have to cut your replacement panels so that the grain is going in the right direction, not just so that they fit on your new material. As a result, you will have about 25% waste.
Time factor: This is another one of those projects that I thought I could knock out in a couple of weekends, but instead it took the better part of 4 months. It is a lot of work. You will want to get your new material with the coating of plastic sheet so that you minimize the scratches while you are working with it (this usually adds a couple dollars to the cost of each sheet). The plastic sheeting comes off once it is in place, which leads to the next issue...
Clear coating: The aluminum that is installed in the new Airstreams is the same as what is used to make the shell. It has a factory applied plasti-coat, and costs a ridiculous amount. Without the clear coat, every time you touch the bare metal, you leave a finger print that eventually becomes permanent. I was unable to find an alternate supplier of aluminum sheet with a factory installed clear coat on it, so decided to paint something on once I had my raw aluminum in place. There is a thread investigating paint-on clear coats. One of the participants had used some stuff, and he got good results in some areas, but a bad finish in others, depending on cleanness of the aluminum. So I recently bought a bunch of this clear coat, and I am looking for a weekend where I have a good three days to do all the prep work and painting. This clear coat paint and prep stuff has cost almost $400, and the whole project could be rendered a disaster if the clear coating goes all wrong.