Should I start with powered flight, or with a glider?
 
Depends on your preferences. I prefer slope planes / gliders, An electric Wing called a bee, 42" and then a 1.8 m (wingspan) called a Passer it is a good size---large enough to be easy to fly but small enough for easy transport. Beginner gliders are lighter, fly slower and are more acceptable to the non-flying community than powered planes---no noise or mess. Gliders are also cheaper (at least the trainers are) than powered planes---no fuel, batteries, starter etc. to worry about.

 Electric Flight is silent and clean so finds greater acceptance from neighbors etc. at the flying field, although some people feel that electrics are not robust or easy enough for beginners. There is a little more paraphernalia - you may need spare battery packs, but you can fly from smaller fields. Power (with engines that use a fuel) will let you fly longer, and your model doesn't need to be as light as with electric (so it's likely to be easier to build ) ; however, you may have to go to a field far from populated areas.

 

 
Whatever you pick, stay away from those sleek fast scale jobs! They look nice and fly hard, and those are the last things you want in your first plane. Stick to the trainers - they might not look as glamorous, but they will make you a much better pilot. And the most important point - no matter what else, try to find an instructor! This is the one thing that may make all the difference between a rewarding experience and endless frustration. R/C pilots are friendly lot, and most will gladly teach you for free.

Are there any organizations etc. I can join for information?
 
Ask at your local hobby shop---there may be a club in your neighborhood. This is the best way to meet other pilots and find an instructor. Most pilots will more than gladly help you out. If you can find a club, for an instructor, choose someone who is smooth in flying his/her plane and that you get along with. Remember, the ones best at flying (hangar or otherwise) may not always be the best instructors.
Join a club in you State.. As I said your local hobby shop will point you in the right direction.. Or leave a message on the forum and we can get back to you.
 
In  New South Wales ,Australia  MAAA  ( Model Aeronautical Association of Australia ) and the monthly newsletter from Miniature Aero Sports NSW Inc,
 
Radios

Q) Since a trainer needs only 2 or 3 channels, should I get one of the cheap radio systems?
A1) Since writing the answer below I am somewhatnow of a differences of option.. There we go even flying for years there are times when you can come across a different point of view. The answer below is still an honest view.. however this can't be said to be the best if you don't continue to fly. The growth in radio controlled anything ( cars, Heli's ,boat and of course planes ) are changing all the time and the price a year ago has drop with some items by more than 50%. There is also a growing area in the RTF ( ready to Fly or use) where a controller and everything is included as the name suggests. When looking at such a item just check to see if the controller meets the standards for the X2 frequencie bands 36 Mhz and/or the 2.4 Ghz if you want to continue and use it on another plane that may well not have a controller supplied and it can alway be a second unit if you stay in the sport. Some I now have several controllers as it is the only way to by that particular plane or car or boat etc.

A) Don't bother with the cheap 2 or 3 channel sets---get a 4-ch system. It will come with rechargeable NiCad  batteries and (usually) 3-4 servos; this is the most popular and most cost-effective kind of system. You can put the main pitch control (elevator) and the main turning control (in this case the rudder) on one stick, which is how most people (and thus most instructors) fly. Talk to a flier or club member before you invest this money.... There are several options  and frequencies .. being 36 Mhz and 2.4Ghz.. the 2.4 GHz is a little more restrictive with receivers to the model of transmitter you buy... Pros and Cons  again the forum is the place to ask.

 
Be aware that you may need to get the same (or compatible) radio as your instructor. but again this is totally on the club you join.... I used my own transmitter , no Buddy box system to learn passing it back and forth....between the instructor and myself.

Another point is the setting up of the plane whether it be powered or slope to have at least a chance to learn you with need to be sure that your model is built correctly and square.. the servo linkages are in the right position, control throws are set and the CG ( Centre of Gravity) is right ( blaanced. I do recommend a Simulator program and you would need to check that the Radio you buy has a trainer port... to connect to the computer.. 99% these days do.

There is a lot about the usefulness of a sim programs,  personally they are not the real thing but when it comes to airplanes, it does help a lot with orientation and the way the plane will react to input... It's a Simulator.. it is ok to crash that is how you can start.

There is a free Slope flying sim... yes I said free so the program it not as hi-tec as the commercial programs and it is basic keyboard control  for Slope flying and it may well help. There are others availiable just do a google search for simulators.

Don't get put off if you don't get it to work at first or even fly.. It is not the easiest to setup and then you really need to have some understanding of slope flying to control.Slope club members , most would have heard of it and many don't use it.. once you get to the flying solo point the program will help with somethings. Stick time (flying time) more you do the better you will get....