For nickel wire, use that which is called Ni200. That is the proper wire to use for nickel-calibrated devices. I typically use 28 gauge.
Use the steam engine calculator to match coil size to your device and to determine the number of turns needed.
Make sure to use enough turns to get the resistance you need; there is a minimum resistance mods will fire at.
For temperature, start at 380-400 degrees and adjust upward if you wish.
Enjoy.