I am currently interested in making a quadcopter ... but some doubts are pinching me... please help me out   
These are specifications of my BLDC motor and esc....

----BLDC Motor-----
Max current: 30A
Max Power: 160W @ 11.1V (3S) / 310W @ 15V (4S)
ESC: 20~30A
Cell count: 3s~4s Lipoly

----ESC----
Cont. Current: 30A
Burst Current: 40A
Battery: 2-4 Cell Lipo
Frequency :  8kHz
SBEC: 5V/ 3A Output

1) What does pwm frequency of esc signifies(WHICH IS 8KHZ OF MY ESC)?
2) ESC's (4 in nos) would be operated by pwm or servo signal with arduino?
3)Does frequency of servo signal in arduino(which is 50hz) has to be changed for controling esc's (4 in nos) in accordance with esc frequency(8khz) in it's datasheet?
4)If so , then how to change FREQUENCY of servo signal in arduino?
5)Is there any library in arduino to control esc??

6)should i buy this IMU for my quadcopter :- http://www.pololu.com/catalog/product/1268   

---BATTERY QUESTIONS----

Let mah and discharge rate of our battery are x and y respectively....

x * y = CURRENT DRAWN BY 4 MOTORS

1)SHOULD I LOOK FOR A BATTERY WHOSE x*y IS EQUAL TO CURRENT DRAWN BY 4 BLDC MOTORS ??
2)If two batteries have same mah and discharge rate product , then should i buy one with higher mah?
3)Which current i should consider in selecting  batteries - max. current specified in datasheet of motor or calculated from it's power and voltage or from ecal???

4)Should I buy 3S OR 4S battery for these motors ??
5)Which brand should I go for?

The 8KHz frequency corresponds to the frequency at which the ESC operates the Three phase inverter circuit.It has nothing to do with the communiction frequency between the ESC and the control board.

As a beginner buy a kk2. Or a naza if you can afford.
use www.ecalc.ch - multicopter calculator.
You dont need any external IMU, the boards have inbuilt.