Hi,
can anyone please tell me whether the below esc suits or not

E-Max, Multirotor 4IN1 ESC(4*25A)
http://rcmumbai.com/index.php/product/multirotor-4in1-esc425a/

What is that BEC-TYpe Switch mode ? whether it supports flysky receiver. ? Also suggests me a low cost 4S battery. amp > (4*20).

Config:
Motor: sunnysky 2216-11 900kv(20A)
FC: APM 2.6

yup you can use this 25A ESC with 2216 motor..
BEC stands for Battery Eliminating Circuit
BEC are of two type linear BEC and switch mode BEC. basics both act as voltage regulator..

1. linear BEC takes input voltage 11.1 (assumption) and reduces it to 6v by resistance and voltage regulator thats why it starts to overheat (I2R loss in electrical language)

2. switch mode BEC (Switching BEC) reduces the voltage by switching supply on and off several times (millions of times per second) thats why the won't heat up and are more efficient than linear bec..
(note- switching bec are not suitable for powering flight controller- red somewhere)
your flight controller will power your receiver not BESC(ESC with a built-in BEC)
regards

Whether Flycolor escs are good, can I go for it. I don't find any 30a esc (4s) @lowcost.

Flycolor 30 Amp Multi-rotor ESC 2~4S with BEC

http://www.vibranthobbies.com/multicopters/power-plant/speed-controllers-multi-rotors/flycolor-30-amp-multi-rotor-esc-2-4s-with-bec.html

Use Hobbyking's F30A great esc just flash it with simonk and it works wonders!!! Its available at vibrant hobbies!

Are you a beginner if yes, i will suggest to buy a cx10 and learn flying on it.

can anyone comment on this

(note- switching bec are not suitable for powering flight controller- red somewhere). Is that true. ?

I read that switch mode BECs are only a problem when connected in parallel on the same power bus. that is why people suggest cutting the red wires from 3 of the 4 ESC BECs. However, this is not needed for the kk 2.1.
SimonK or BLHeli firmware flashed ESCs are supposed to be better for multirotors. You can get them pre flashed or take the effort of flashing them yourselves.

I saw people facing issue with flight controller when they are use switching bec to power flight controller...

Which flight controller was this? Had they cut 3 of the red wires or not? Or was it a stand alone BEC?

He was using ESC with switching bec naza v2 flight controller (with red wire attached) And he was facing arming issue.. Problem resolved after removing red wire from all the esc..

you can use your switching BEC to power a FC just add a capacitor(high capacitance) in parallel to the power line(between red wire of the BEC powering the the FC and GND(black wire))  

But I think capacitor will not filter harmonics. You need t-filter for pure DC output.

I think a capacitor might not be enough...Don't know much about t-filters...you can also try adding a ceramics caps(100nF) which are better in dealing with noise then electrolytic capacitor

Actually capacitors stores voltage (don't act as filter alone) and inductor stores current ( both combined act as filter. Different filters are designed for different setup ( high pass , band pass, low pass etc)
But if you are using naza or apm then you don't need bec to power fc they have there own power source... Just remove red wires from all esc and fly...