I've successfully finished home builds using acrylic aerosol paints as well. Go to your local halfords and you will be able to get good variety of colours to choose from. I found halfords to be a bit more expensive than my local auto shop (£7 vs. £3 for the same stuff) but I was only after black paint which is more likely to be stocked by the smaller independents.
All of the paints I used claimed to include UV inhibitors which are supposed to stop the paint from yellowing (I don’t know if you can buy them without. I couldn’t see any).
I would recommend spraying about 4-5 colour coats then spraying at least 12 topcoats of acrylic clear. You need to spray so many coats because when you come to buff and polish the paint, you’ll take off quite a few players of paint. I managed a nice glassy finish using this method.
Metallics are a bit harder than plain colours. Rather than explain it all, your best source of info would be to browse though the rerannch forum:
[url="http://reranch.com/reranch/"]http://reranch.com/reranch/[/url]
Although they deal with American products and talk about using nitro, the principles are the same.
If this sounds like too much work try asking your local car sprayshop to spray it for you (if you have one!). I know people who have had success this way