You mean, the power ignition for the power for the camera? or the power for the PIE?

I do not know what camera you are using, but most cameras have a very low consumption requirements, so drawing power from rear seat adjustment might be OK.

Power for the PIE should be directly from the battery (with a fuse, of course). In order to avoid draining your battery when the car is off, you need to tie that to the ignition - and again, using a relay, to isolate the car's electrical/electronic system form your aftermarket system.

You always have to be mindful of the draw requirements of your equipment - if you use the too heavy of a load, you might get some gremlins...

Are you able to obtain those relays in your country? these are very common relays, in the US they are sold in Radio Shack (and in the US they don't usually sell electronic components, as we are used to things already made for us)