You really have come to the right place, but no one has answered any of your questions yet...so, I'll do my best.
No. Not everyone freehands their art. It depends on many different factors. What you're doing, what you're working on, how big the surface is, etc., etc. Personally, I sketch on paper what I want, then I decide if I can freehand it or not. Normally, freehand will not give you crisp lines (there is SOME over spray). Some will use frisket paper, sketch out the drawing, then remove the sections to be sprayed. Then go to town. The hot item, tru flames, is done freehand. Some use circle templates and some use sporatic shapes exclusively.
The above mentioned magazines in the previous posts are good. Do a google search.
www.airbrushtalk.com is a good one. Also,
www.airbrush.com has a LOT of tutorials (How-to-guides). Airbrush Action magazine is a good one. All in all, if you type in a general question into google or other search engine you'll find what you're looking for. Also, one of the best, click "search" at the top of the page and type in your question. For example, say you want to know something about your Iwata HP-C. Click search, then type in "Iwata HP-C" and you'll get a return of all the forums where HP-C was mentioned or discussed. Then, if you can't find what you're looking for, ask a more specific question.
Post your work and we can critique it.
Hope this helps!