#1) Who knows about rumors.

Even if a new came out I would be perfectly happy with whatever I bought now. The only so called "improvement" I have heard is Maybe thinner and maybe Blue-Ray drive. Cool but would not stop me from getting one now if I needed it now. Just my .02 cents.
#2) Once you set up iTunes on the new iMac you should just have to sync. You will probably have to "authorize" that computer but it is fairly painless.
#3) Not that I am aware of. (see above)
#4) See Above
I switched to all Macs 4 years ago and have not looked back. I use both my iMac and two other Macbooks for my two businesses. I have Parallels installed but only fire up Windows when I ABSOLUTELY have to.