eyetechy

Hi everyone, i have a few questions i thought you guys could help answering me. I have one Team Associated 18R Niteline and i'm about to do one upgrade on my motor and esc. I got this combo from Team Orion (ORI28121 and ORI65017), basically is a brushless system with this settings:
Motor:
KV: 7500RPM/V
Operating Voltage: 6-12 cells (NiCD/NuNHl) 2-3 cells Li-Po
Max. effciency current: 10-19A
Peak current (5 sec): 23A
Resistance: 0.038 Ohm
No load current: 3.77A) 23A ESC (Input voltage: Ni 4-8, 2-3 Li; continuous current: 25 A peak current: 30 A; BEC: 5 V / 2

ESC:
Input voltage: Ni 4-8, 2-3 Li; continuous current: 25 A peak current: 30 A; BEC: 5 V / 2

My first question is, i can see that i can use 2 or 3 cell lipos, so this means my ESC is ready to stop my car or something when the lipos get low voltage?
What kv means on a motor?
Is this too much power with stock plastic spur gears?
This car has a 55t spur and a 15t pinion, should i keep this gear ratio with this new motor?

My last question might sound pretty dumb, but i found that when using the 18r if i turn the throtle trim full clockwise and hit the gas the car almost doubles the speed comparing to the normal point wich is just before the car starts moving, 12kmh more to be more specific.
Is this normal? i shouldn't do this?

Thanks in advance, really appreciate!!

Eyetechy