Firstly if you are making small parts its far better to use a small high quality spray gun, as this will make spraying clear coat a lot easier, and with practice you should be able to get a pretty good gun finish, needing only final buffing. I use one of these: http://www.spraygunsdirect.co.uk/product_info.php?products_id=2076&oscsid=fa052587482650bbea13f5899e63e0ad
Unless you are making pretty large items such as car hoods, then stick to a fluid tip of 1.2mm, as anything bigger is going to mean very thick coats and a strong possibilty of runs. Very good results can be achieved if you spray a couple of heavier coats of 2k that has not been thinned, and after allowing each coat to flash off, one final finish coat with the 2k thinned a little.
But if you don’t want to practice on expensive parts you can do what ClassicBike says and get a mini gun with a 1.2 tip and reduce the clear coat by 5%.