Actually I can't leech my pet all the time since it's tanking a lot but I'm doing it whenever possible and I'm definitly going to try your routine.
I do have power issues especially when I run out of power and wait to go up again, that's normally when I can't leech my pet or I would kill it. My power bar just moves up a bit only to go down again.
Maybe it's getting better with 1. the black heart 2. changing to another pet 3. hold back with casting 4 try to use only one pet buff.
The thing that was mentioned above irritates me too a bit. I cast some 3 spells and I'm already getting near to half of my power, having a Int 135 and some power ups too. I guess the list of mana cost per spell/ DPP is becoming more and more important.