I started out with a pressure system as well. Thankfully I had a friend that was able to make a heater block for it. It was a little tricky to get started, but when it did, it really threw out the heat. Eventually I got tired of the hard starting and moved to a siphon CK kit. It certainly is the way to go, but yes, it involves more than just the CK kit (constant level tank or meter pump, compressed air source, etc...) which all cost money and it can add up quick.
I have never had to vent my holding tanks, so I don't really have any suggestions on how to handle that. Good luck with your project!