ORIGINAL: patnchris
1. Is one required to have a license to fly planes?......I realize that for many of the larger, more powerful planes, it is logical.
No. The AMA 'license' permits you to fly in AMA sanctioned competitions. There is no requirement by any governmental agency for a license to fly. AMA membership and the membership card are often referred to as a 'license;' AMA promotions in hobby shops proclaim "Get you AMA License Here,"and it was even printed on the card until a couple of years ago.
AMA chartered clubs are required to mandate AMA membership on all club members. It appears that an AMA club has a use agreement with the park where the flying site is. That is why a 'license' is needed to fly there. Some public entities prefer to deal with clubs rather than individuals regarding uses like model flying. They expect self-policing from the club, and also may require the liability insurance and co-insurance; the club and members generally find this easiest to obtain from AMA.
2. I only plan to fly electrics. For now, probably park models.....However, what determines a park model, from any other
The distinguishing feature(s) relate to compatibility with the park environment. Quiet operation (hence generally electric powered), and non-threatening to other park users, which infers low mass and velocity. I wouldn't personally want to fly anything with kinetic energy over typical park 'missiles' like footballs and frisbees, i.e., under about 12 oz and perhaps 40 mph. AMA has proposed a program intended for park flyers that would weigh up to 2 lbs and travel at up to 60 mph. There is no broadly accepted definition of park flyer and there probably never will be, until some organization (AMA or other) sets arbitrary limits based on an insurance provider's guesstimate of liability risk.
3. At some point in time, I would like to build my own planes, from kits and maybe, my own design. Where does one find out what restrictions there or, regarding this.
There is a de facto restriction on weight of 25 Kg, set by an international organization of commercial aircraft operators (ICAO), and agreed to by the US, represented by FAA. FAA has not yet felt the need to enforce it, leaving that for the time being with organizations like AMA. AMA restrictions conform to this 'guideline,' though exceptions are made subject to specified controls. Suggest conforming to the guidelines found in the AMA Safety Code, unless/until you find them too confining. FAA does have control of the airspace, and I expect if you reach a point where AMA guidelines are going to be exceeded, you'll have to deal with FAA directly, in which case the answer is likely to be NO.
Abel