i did suggest the idea of additional torque but that would be achieved thru the gearing... changing the rear sprocket and/or motor sprocket.
Ah refers to capacity. the higher the capacity, the larger the physical size of the battery. 7,8, 9, and some 10Ah batts are identically sized. 12-15Ah batts are bigger and heavier.
the stock E300 comes with two 7Ah batts. i'm very close to your weight. i've rode on my kids' E300 which has been upgraded to 9Ah batts. 30min runtime is do-able.
now to get over 20MPH requires overvolting. overvolting = higher power consumption. i dont see 30min runtime maxed out throttle on an overvolted setup with 7Ah or even 9Ah batts.
to overvolt you'd need to mount a 3rd battery somewhere. if you want 30min runtime or more now you have to plan on installing a larger battery than stock.
lipos were confusing to me too, before i started using them. do you have a smart phone? i'm still using a flip phone and to me smart phones seem complex but i think 90% of the population uses smart phones, including my kids