@dubliner: I would suggest to wait till you get the device and check the build number. Maybe yours will work out of the box?

Next, you may want to get SD card. Onyx is blessed with having a slot for it - its great to keep your photos, videos, and other larger files. In addition, it allows you to make a snapshot of your internal storage and restore it later with TWRP. For reference, I use 64GB card - 20 GB is used right now (2 backup, photos/videos, maps).

Cannot help with the other questions, unfortunately.