I don't even have a cooler on mine.
In a nut shell here is what I know/have been told.
Less restriction is always a good thing. When doing full hydro the pump suction line needs to be 24" or less and minimum of -10. Pressure line to the orbital can be -6 but -8 is prefered. Pressure lines to the Ram should be -6 and the return from the orbital to the resivior should be -8.
Run the system without a cooler at first. If the fluid exceeds 190 degrees easily then you will want to plumb a cooler into the return line. It should not be a stacked plate cooler but instead a fin and tube cooler or straight through design. The tube and fitting size of the cooler should be at least -8 size if not larger.
There was a lot of time spent on the phone with Howe when I did my system 4 years ago and it has paid off for me big time. I have their full system and have yet to find a major flaw.
I sometimes want a bit more pressure out of the pump and could get it with a simple change but it is not important enough to me to take the pump out and work on it.
Howe also pushes to use their fluid OR GM power steering fluid. I use the GM stuff and love it as well.
There is your full hydro info from me.