1) Download the service manual.
2) 60K if towing 100K if not. Dipstick and fill plug are on the body of the transmission itself. The pan can be dropped and you can flush,either one.
3) 100K is reccomended, but sooner won't hurt. Use OEM plugs.
4) Not sure others might know. There are only two options.
5) Transmission acting up 1st to 2nd, 2nd to stop, etc. Can be cured by having the TCM flashed at dealer. Wind noise, minor squeaks, etc.
6) None that I can think of.