Front and rear disc. Purely because the break system will not be affected if you buckle you wheels.
Also discs provide better stopping power. Ever wondered why every bike over around £250 comes with discs, its because v-breaks are shocking.
Depends... Where & how will you be riding? Disc brakes are better for extreme off-road conditions and rainy conditions. V-Brakes good enough for everyday street riding & light off-road riding. Go one way or the other fully. Either all disc brakes or all V-Brakes. Good V-Brakes are better than bad or cheap disc brakes.