Hi Philgib,
If you want to know everything on battery and battery charge I recomand to look at: https://batteryuniversity.com/
You dont need a 18650 to get 1000mA out, it exist flats one which should be much smaller.
One parameter which is important is the C-rate and how much peak current you need. Generaly for a 1000mAH battery you can get 1000mA peak load and charge it at max 1000mA (to simplify). But for drone application you can found battery with 20C discharge current (but price is not the same!).
Regards