Planning Xray XT8

[Jabe]

So i sold my Hyper ST and got Xray XT8, its not '09 but it will do it.
My plan is to keep weight in minimum as possible.
Something i have planned to use:
-RC-Monster 808 motormount (if it fits, just getting info about it)
-HPI Vorza battery tray for its adjustability
-Tekin RX8 and maeby buggy motor (i have plans to get Xray buggy and be able to swap electronics)
-mechanical brakes with miniservo

Cant deside about battery, should i use 4S or 6S and how big, atleast 15min.
Comments about choices??