I know it all sounds good to save some time and do the prep work yourself, but its the prep that can make or break a spray job. If you don't have a well prepared body to start with, your paint won't just hide it, it'll highlight it! There is a reason it costs you more to have the bodywork done properly but its soooo much better to save up the extra and get it done right. I see too many cars driving around with horrible looking "fresh" paintwork, and atleast 9 times out of 10 its just down to trying to save money on 1) preperation and 2) paint materials. Don't skimp on the brand of paint that get used either. For the sake of a coupla hundred bucks savings, just buy a well known brand paint and enjoy a good result.