It's tough to say as everybody is different, but in my opinion I would go down the full set route. If you start mixing and matching iron or wood sets you're going to make a difficult game much harder for yourself. That doesn't mean go for the same brand throughout your bag, it's fine to use Ping irons, Taylormade woods, Cleveland wedges, etc, but keep each club type as similar as possible so that you can develop a consistent play style rather than adding the mental burden of having to remember to hit different clubs in different ways to get the desired results.
Golfbidder is very good and there are a number of highly reputable second hand dealers on eBay too.
