The lipo specs should exceed that of the esc. The esc specs should exceed that of the motor. But you have to stick with the acceptable voltage.
- eg. A pack capable of delivering 180A constant would suit an esc that can handle 150A and the motor 120A. Put it the other way around with the motor at 180A and the lipo at 120A and you'll have nothing but very bad things happening.

Don't be tricked by high price lipo's being quality, some have good warranties that are added in this price.
Get packs that are tried and tested by many users and happy with them,

C ratings are questionable, one companies 40C might be weaker than another companies 25C.
Personally if i was upgrading motor and esc later on i'd get new lipos and if the old ones are still good, sell them on.