Also i am looking at the link Domush gave to the paint on Ebay and also Duplicolor paint on amazon. How much paint should i expect to use on a ranger? And clear?
You will likely use about two quarts, which means a gallon is both the cheaper and safer bet. Being new to painting, the gallon will also allow you to do a few practice panels.
When practicing on a panel, the most important part to practice is getting the air pressure and fan spray correct, then training yourself to move at a constant pace and stay perpendicular (as much as possible) to the panel. A few youtube videos will get you educated in that area a heck of a lot better than a bunch of text will.
A gallon of clear will go a long way, and is always handy. In fact, next order I make will have two gallons of clear, as it works really well over rustoleum, too. In short, if something looks dull or is easy to scratch, clear coat makes it look new again in addition to protecting it from scratches/rust.
Clear coat is also great for playing around with additives. Say, you want to make something visible at night, you can add glow-in-the-dark powder to the clear and poof! You just make it glow-in-the-dark! The same works for pearl paint jobs, the pearl (or metallic flake, or..) is just a powdered additive.
If you are simply painting some yard items, I'd recommend starting with some rustoleum or valspar, then finish it with clear. It is very cheap ($9/qt) and will get you practiced up for the 'real' stuff. I painted my entire tractor with those paints. They also thin really well with acetone (which flashes quickly, making it easy for beginners to prevent runs).
As for repainting, a full degreaser wash and a quick scotch-bright pad over the paint, followed by a light brushing with a shop cloth (tack cloth if you have one) is all it needs. For rust, sand it out or use a rattle can of rust converter, lightly sand, then prime.
Primer varies in thickness depending on whether you want to fill in scratches or simply prepare bare metal for paint. Buy what you want. I like high fill types of primer for equipment because it adds an extra layer of protection from deep scratches. Heavy primer will require more clear coat if you don't sand it, in order to smooth over the grit it leaves behind from the filler additives in it. For auto and important stuff I will use thin primer and hand sand using sand paper wrapped around a carpenter's pencil. The finish you get out is proportional to the time you put in for prep.
That should get you started. Be sure to watch 10-15 painting videos on youtube, as they will walk you through it nicely, especially getting your paint gun spraying correctly. And, of course, have fun doing it! It's quite enjoyable seeing before and after photos, as you noted with the finish mower. Painting is very gratifying if you aren't trying to be perfect.