I'm sure that this has been covered before, is there any thread or links I can look at that explain what prep needs to be done to the aluminum before spraying? What primers need to be used and what paint I can use?

came up last week - search for U´pol or upol and-or etch primer

Here you go
http://www.locostbuilders.co.uk/viewthread.php?tid=86275

Maybe this is also usefull:

plasticpaint

It's not painting, but coating with vinyl, it's a dutch site, but maybe there's also companies in the uk doing this. The most used form is with clear vinyl to protect from stones etc...