First of all, go to a real paint store (not Home Depot) and ask for a list of painters. You would do this after you have checked with your friends to see if they know any painters. That is really the best way to find a painter. That is how everyone finds me. I don't have references and nobody ever asks for them. Stay away from the yellow pages if at all possible. The estimate is usually exactly what the final price is unless unforseen things come about. As these unforseen things come about, you should be notified by the painter or given the opportunity to sign a change order. Yes, the proper way to paint an aluminum sided house is to power wash and paint...probably 2 coats of a high quality exterior acrylic paint in a satin or better sheen. IMO it looks best sprayed on but spraying is not always feasible. A primer is really not necessary for the siding itself but may be used on wood trim and windows. The painters should cover/remove anything that you don't want painted. You shouldn't have to do anything if they are real pros. I would say that a good paint job should hold up at least 8 years and most painting companies will warranty labor for 2 years. You should be able to prime and then apply finish coat about 4 hours later depending on drying conditions.

Sherwin Williams has a website with tools like that I believe. Some of the other paint mfrs do also. Now, hold your hat, but remembering your un-intended lime green kitchen ; ) how about getting one of their color consultants to come out to the house, too :) It's only about $40 and they even deduct it from the cost of the paint. BM may also have similar assistance with color consulting. Wayyyy too big a project and investment for errors. Do your homework with photoshopping and such first, but that can only give you an idea of what you like or don't like. The colors aren't very accurate at all when you get down to specific paint colors. It's just a tool and, unfortunately, not really magic!

Good choice in brand, not so much in sheen. Personally I would never use flat on an exterior, flat is a good dirt catcher.

clean with tsp and scrub it with a deck brush and repaint with flat paint since you dont know what product was used