1. Yes, totally worth it.
2. Answered above. Personally I rode without one in late November and early December. Right now my local cable is about 40, so high 60's sounds lovely to me
3............
Definitely start on the beginner cable.
Can you do a standing dock start?
Are you goofy or regular? Goofy is easier as you just take a heel side edge around the corners.
It takes time to get a feel for the corners, the 90 degree ones can be very unforgiving.
Have you ever hit obstacles?
You'll pick it up pretty quickly, I would not bother with a kneeboard, you can figure out the corners on a wakeboard, I would only suggest a kneeboard so someone who is a complete beginner.
If you are a competent rider and you've never ridden cable / hit obstacles, I think you could ride the beginner cable for an hour an not get bored. Small rail, little kickers and wedges regular and switch, try 180's , 360's .......
Try to get as much prep, waivers etc. completed before land and watch as many instructional video's as you can.
Standing start:
https://www.youtube.com/watch?v=__nZW2ZxegU
1st: osbtacle:
https://www.youtube.com/watch?v=wobi1_a36gU