Ideally you should buy good quality 18650 brand name cells like Sanyo and Panasonic. Example Sanyo cell
here. Example
Panasonic cell.
The problem with cheap 18650 is that they are frequently re wraps of salvaged laptop batteries, which are not ideal for higher drain applications like planes.
The nano goblin pack is available separately, you could run an FT goblin on it if you built light and kept the motor and prop sizes close to the OG goblin ones.
You will also have to solder your own packs if you make them for other planes, ideally you use a Capacitance Discharge spot welder for that, they cost $$$ but don’t involve heat build up. Soldering lipo of any type is potentially dangerous, you don’t want to get them hot or damage the casing. You can use a soldering iron but you do so at your own risk.
Lithium ion cells are not suitable for every application, the Goblin is pretty efficient, generally a light wing loading pusher design with a small motor will work with them quite well. They are not capable of the massive discharge rates of pouch lipo cells.