I would personally recommend to buy a good dual 18650 mod and get it over with, even if you don't use all the watts etc. Assuming your ok with a bigger box. It will stop you from wanting to upgrade all the time and can last a very long time.
Mod: IPV3 LI, or IPV3 LI VR, or Sigelei 150tc.
Batteries: Samsung 25r
Charger: Nitecore I2/D2/I4/D4