Never had a problem when ordering from Aliexpress, or any Chinese seller, except for a few problematic ones.

For the 18650s, I would just get the Sofirn SP31+18650 combo so you can directly use it with the light, which is nice, and you don’t have to worry about shipping.

Fortunately though, since the lights I recommend aren’t particularly demanding, I would get these additional 18650s from PKCell:

They sell legitimate cells.