Finally am back to business almost after a year.some inputs from you all will be appreciated                 
Specs for reptile 500 quad

Frame- reptile quad 
Motors-2216 810kv emax
12x4.5 props
ESC -simonk  25amp
Battery-4200mah,20c,3s     
FC-APM2.6+ ublox6 gps+power module   
                                             
Fpv::   
SJ4000- for fpv output and recording
Monitor--Boscam RX LCD 5802 7"built in rx and battery
Av TX- avionics 400mw from rcbazaar
Radio- 9xr with orange module and rx

I think you should get a higher C rating battery .. rest all seems fine

  i already spent too much exceeding my budget.so thought of 20c only,it will not be a problem i hope so

20c should be sufficient for smooth flight and AP. But don't try too many punch outs though.

thanks ashimda for the input