The maths to figure out the amount of power you are going to need is very simple, the formula is P = IV, which is then rearranged to I = P/V
Basically, the power draw in watts is divided by the mains voltage you are going to be using (which will vary depending on where in the world you are)
Beyond that, you just need to make sure that the circuits (and extension leads etc..) you are using are rated to deal with the amount of current that is going to be going down them.
If you can, it's nice to be running of a separate breaker to sound power, to make sure that you aren't going to cause each other problems if either of you trip a breaker.
In three-phase systems, it's usually considered good practice to sit on a different phase to sound if you can, as sometimes (more with conventional dimmers than with the SMPS used with most LED's) lighting gear can create harmonics on the live, and put noise on the neutral that can have negative effects on the PA system.