The rule with compressors is simple, you can never have one that is big enough. And sure enough, the one you bought isn't big enough. Well, it is actually, but just barely so.
Depending on what gun you pick up you may not have enough compressor to run it well. You definitely do not have enough compressor to shoot a car with a BC/CC job, which would require a full sized gun. You have plenty there to shoot a motorcyle though, particularly if you pick up a nice little touch up gun to go with it.
On compressors: In the best of all worlds you would want an oil-less compressor. Even the slightest oil contamination of your air when painting will result in fisheyes. Oilless compressors are hopelessly noisy though, and to tell the truth most of the ones that are sold are pretty poorly made, until you get up to the ones that cost mega-bucks. Those compressors you see with the double little hotdog looking tanks or the squat little pancake looking tanks, those are made for running construction tools, nailers mostly. Small Compressors that use an oil bath are common and you often see them hooked up to 15 or 20 gallon tanks. You also see them atop 50 gallon and larger tanks and of course they get much bigger than that. If you have enough storage capacity you can shoot anything even with a small capacity compressor. When you buy one something with about a 30 gallon tank makes it easy to paint bikes and possible to paint cars - small cars..
If you buy an oil bath compressor you will need to put a good filter in your air system and to paint vehicles you need an air system. Just running a hose off the compressor will work, but it will not work well. Your air system should be designed such as to capture all the water that condenses in the system, to filter out oil or any other contaminants, and also allow you to dial in the line pressure you prefer. It does not cost very much to put together a system, just the price of some pipe, some fittings, and a couple of valves. E-bay is the place to hunt for a good deal on a filter. You can find suggestions for system design all over the internet. Just make sure you have at least one tall vertical run with a drain at the bottom and you'll do just fine. Some guys make theirs out of coper pipe (expensive) and some make it out of PVC (cheap) and some just about anything inbeween (mine is iron water pipe - in the middle price-wise).
For whatever its worth there is a big change going on right now in automotive paints. Traditional Automotive paints are hell on air quality and the chemicals they emit as they dry are hell on the human body. Their days are numbered. More and more laws are being passed to limit the extent to which a person or company can dump trash into the air. That is a good thing but its going to kill some types of paints. Manufaturers are switching to water-based paints every day, and its just a matter of time until that is all that is available. I'm just about done painting so I don't really care, but I have to tell you that of the several jobs I did using water-borne paints a couple of years ago were, to my mind, very disappointing. Back then I used Auto Air Color paints and it is my understanding that they have completely reformulated their line since. I'm sure the stuff has got to have got better since I used it, because it couldn't have got any worse.
Paint guns. If you want to buy a cheap gun look for a siphon feed (paint pot on the bottom of the gun) and rest assured that you are using an out of date antique that very well may have a nozzle on it big enough to shoot mud. Once again it is a matter of air quality that gives us our modern guns. High Volume Low Pressure (HVLP) guns are the industry standard now days for automotive refinish. If you've been looking at the market for guns I'm sure you've noticed by now that they range from cheap to gawd-awful-expensive. Gawd-awful-expensive guns are worth every single penny they cost, cheap guns generally are not. There are a few exceptions to this rule though. Lots of guys rave about the Harbor Freight "Purple Gun" which I understand cost less than $25. All of my guns and airbrushes are made by Iwata. They are of the Gawd-awful variety. Sata guns fall into that same catagory. Cheap guns go by many names, pretty much anything the Chinese can spell. There aren't all that many guns in the middle, but you can buy a nice gun from Sharpe or Binks that shouldn't cost you too much. If you intend to do general automotive type finishing I'd suggest you get something with about a 1.4 mm cap, you'll find it will work with just about anything. If you plan to shoot cars get a quart (or liter) cup, if you are just going to shoot bikes you can get away with half that. Do not overlook touch up guns if you are just going to do bikes. Look at the spec sheet for whatever gun you plan to buy and see what size fan it shoots. Presume that when you get one in hand you'll only get about 80% of what they advertise when its finally adjusted right, but for bikes try to find one that can shoot at least a 4" fan - standard full size guns shoot a fan about a foot tall. Once again, as a personal note, the small gun I use is an Iwata LPH-80 (1.2mm) that when adjusted for a very even pattern will shoot a fan 4" tall. That is a very good size for motorcycle parts. I also have an Iwata gun that is about 3/4 the size of a full-fledged gun. My Iwata LPH-300 shoots about a 9" fan when adjusted, compared to a full 12" fan for the LPH-400 (full sized gun). With the 3/4 sized gun I can clear-coat a fender with one pass of the gun or a tank with 2. That means I get very even coverage and very fast application. Now think about this. If I was shooting a bike with my guns I could use your compressor. First I'd shoot the fenders, and then I'd stop for a couple of minutes while the compressor kicked on and refilled the tank. I'd shoot the tank next, then wait another couple of minutes before shooting the oil tank and maybe a helmet or two. The point being that even a small compressor can do it, you just have to plan the job so you don't run out of air in mid-part.
So from where you are nowhere's what I'd suggest to you. First go ahead and put a pipe system in where ever it is you plan to paint. Make sure its got a good vertical run or two, good long slanted pipes, a good water trap, and a pressure regulator/gauge in it somewhere. Keep your eyes open for an old dead compressor you can pull the air tank off of. Plumbing a second holding tank into your system (with a water drain) can really add a lot of capability for very little money. Next start looking for a gun. I'd definitely buy used if I were you and I'd buy the best gun I could lay my hands on, but if you don't want to spend that kind of money take a good look at some of the guns by Sharpe or take a chance on one of the HF guns if you like.
Oh, here's a hint that is going to save you thousands of dollars and much heartache; always shoot test panels.
