IF you are going to buy a non digital radio just get the 4 channel and save the extra cost for when you decide to buy a computer radio which you are going to want eventually more than likely.
Unless you turn out to be a person who only is interested in trainers and cubs(which is fine) you are NOT going to be satisfied with the 6EXA. I 100% Guarantee you you will not be satisfied for long, no matter what the other guys say here. If you intend to move up to any kind of (relatively) serious aerobatic flying and get into planes outside of 4*40's, Stiks, .40 sized planes and small scale planes its not going to work for you. One good thing is that the 6EX is an ok radio and its not much more expensive than the 4Y so you really arent losing anything significant buy buying it but it wont be your last computer radio I promise you. You WILL want to get a better one within 6 months if you develop at all as a pilot.

OK,

It will take a servo to drop a parachute, bomb, etc.

How long it takes you to learn to fly depends on you. Some folks I have trained have been capable of soloing in about 3-4 days at the fields making 3-4 flights per trip. Others have literally taken months of lessons 1-3 times per week. Everyone eventually gets it and moves on to fly on their own if they really want to learn. A good trainer wont cut you loose even if you can takeoff and land intil they are sure that you can handle the plane in the typical abnormal situations and you demonstrate the ability to fly the plane with good control no matter what direction it is facing relative to your point of view.

I would say if you are an average, younger (15-45 year old), computer saavy person with pretty good hand eye coordination you will probably learn to fly competantly in 4-8 lessons which can probably be done in 3 weeks to a month.