You will be ok with 2 Lipo, 6s @ 20Ah in series are working for me since day one, I added others to have more flying time and to have a change (double session without having to wait).
18650 to me are good just for 14s (higher voltage=more speed) and to really get some serious run time, but 18650 are not even closer to Lipo as performances, the voltage sag way more and the total capacity drop quite a bit, if the cells are stressed by high amp request as we do. So Li Ion ok for big pack, ok for hi voltage and ok if you don’t care/don’t know what you’re doing, they’re safer in that case. But 2 Multistar 20A made lot of folks happy here.
If you go geared, expect 50-70A max from batteries, let alone motor current at partial throttle which is another story, you don’t care about that when dimensioning battery pack ( you better care when sizing esc, cables and motors, instead!)