1/8" pilot hole should work well for you.
If you use 1/2" thick drywall, the studs are 3/4" thick, so you can fit in up to a 1-1/4" shallow box. Just be sure nothing protrudes into the pocket of the door/wall. Consult your local electrical codes for code compliance.
Just go to homedepot.com and search for “152480HD” and “153680HD”. They are available online.
No, those would have to be purchased separately.
Yes, you can. That is what I did
The width can be pretty flexible. Minimum of 74" inside to allow for a full door opening. Maximum isn't that important other than the wider that you go, the bigger the header that you will need. A 6' header will need a decent size beam. I used a 4x10 DF because I had one on hand and I had the room for it. Check your building code. I don't remember the exact height but it is clearly spelled out in the instructions.
Yes you can, but since it's designed for a standard 80" door, you'll need to cut the included studs off by 2" or you'll have a large gap at the bottom of the door.
Yes, if you use a 1-1/4" shallow box with 1/2" or thicker drywall, it will fit.
Unfortunately, you would just have to order a larger pocket door frame. We don't sell extension kits.