Mesh and wire is all preference.
The general rule of thought is the lower the grade/density of the mesh, i.e. 325 is used for VG heavy juices and the higher the grade, i.e. 500 - 600, is used for more PG based juices.
I typically use 400 since it's a bit more in the middle of the road.
Kanthal depends on how many wraps you prefer and ohms. The higher the gauge like 32, 34, or 36, the thinner the wire and the more resistance you'll have. The lower the gauge like 30, 28, or 26, the thicker the wire, and the less resistance you'll have.
32 gauge is a good starter wire. More wraps of it will give you more resistance so using it on an electronic, regulated
device like an eVic will probably be a bit more beneficial.
If you use less wraps, you'll have less resistance, which many regulated devices won't fire if they are very low. However, there are individuals like myself who like to wrap very low resistances on mechanical mods, since they're unregulated and will be able to push beyond the amp limit.
FYI: The RSST is one of the easiest gennies to rebuild. Good pick!