Welcome Tim, glad you joined the forum!
As you may have read elsewhere, the pressure system was easy to do, although it isn't the optimal situation for burning waste oil. When my furnace lit, it would provide great heat. The waste oil burns nice and hot! The problem with the pressure system was that it was difficult to light. I had to turn up the nozzle heater very high to get it to light, then turn it down once it was running for a bit. I never did get it fully automated, starting and stopping on its own.
In the end, I wish I would have spent the money on a siphon system right off the bat. The CKburner kit works very well and fits nicely into commonly found Beckett burners.
Is there a reason you dont want to go the siphon route? My initial thought was that they siphon system was more elaborate than I wanted to get into. Sure, you have to have the float tank, an air source, etc... but none of it is too difficult to get working.
As for the cartridge heater in my pressure system, I used a Vulcan TB388A. I ordered it from Grainger. If you do a search for the model number at grainger.com you will find it.
The PID I used had a built in relay, so basically it was just to run power to the controller, and run power to the cartridge, using the connections on the PID similar to how you would wire a light switch into the circuit. You can think of the PID as a switch that turns on and off as it meets its temperature set points.
Hope that answers your questions. If you have any others, just let me know.
Thanks,
Russ