Rak2245 with rpi

how much power is required by 2245 pi hat with rpi working together ?

It is same with RPi.

Rpi is 2.4 amp max.

5 x 2.4 = 12w, will that be enough power ?

Yes, i think so.
Usually, we use 5V & 2A/2.5A, and it works fine.