Bill is right, get a touch up gun. I have the smallest auto paint gun that lowes sales. I bought a cheapie to begin with (little over 50 bucks) and I honestly love how good of a job it does. It puts out just enough paint to do the little pieces such as doorhandles and the like.
The most important part of painting anything is prepping it properly...i couldn't count how many painted pieces i saw at showfest that just looked like absolute :crap:
The thing i do is...when I think i'm through sanding, i'll wash the piece off, put it down, come back in 20 minutes and notice how much I actually missed. After i do this two or three times the pieces are smooth and pretty paint ready. Alot of people will say to use 1000 and 1500 grits before painting, to me this is a complete waste of time. I typically use 100 to knock the texture down quick, then 220 followed by 400 and sometimes i'll finish it up with 600, but 400 wet is usually a good surface to paint over. Those 1000-1500 grits are great after you spray your clear to wetsand the paint to get rid of imperfections.
I didn't know if i could do it when i started either, but just take your time and the pieces will come out great with the proper prep work. The key is the prep, i cannot stress that enough.
Also, before you paint you'll want to use a good plastic cleaner and an adhesion promoter, especially on the plastic pieces. I've personally never painted metal, only plastic, so i cannot help you there.
Here are some pieces i recently painted for a friend of mine
Tomorrow I am spraying his bezel and a few more interior pieces for myself, i will admit, once you learn how to do this it is very