1.) JR voyager 30 is a nice heli, but it's little bit underpowered for 3D ... but you can upgrade it later
2.) I don't think it would help you that much ... helis and planes are totally different ... being able to prophang and torque roll might give you an edge over somebody who has never flown anything before, as you will learn to control the heli in a hover much quicker / easier.
3.) it's fairly realistic, but the first time you try to hover the real thing, you will notice that there is a difference between it and the sim. But, don't throw the sim away ... it helps you hone your skills. (and being able to hover, nose in, tail in and land is a bonus)
4.) See Quattro27 post

Being able to prophang, I assume you already belong to a club? Have a chat to one of the heli pilots at your club (even if it is ... in a tree)