Hexapod battery selection

i am building a hexapod.. it have 6 legs.. 3 on either side.. i have to control 18 servo motors
simultaniously.. 3 for each leg.. for that i am planning to buy an arduino mega 2560.. will
it work well?? can i send signal to all 18 servo motors simultaniously
using this board..?? can i connect all of them directly to this board?? which battery should i use to power arduino mega 2560
for providing signal to servo motors??