OK let me see if I can answer everyones comments and suggestions in one post!
First of all, the idea of using both the kettle and HLT to create hot water to use for sparging etc is a great idea. I will re think the connections a little to see if I can get it to work automatically. It sounds like it will save a good deal of time and be much more efficient.
yes, I plan on insulating everything I can to maximize efficiency. So all 3 pots will be insulated, and hoses etc where I can without interfering with normal operation.
We plan on hard plumbing everything all the way out to male 1/2" SS QD's. They looked nice because they had no internal shutoff valve and looked easy to clean. Then we are using the Hi temp plastic 1/2" tube to make F/F "jumper" cables to connect everything together.
I picked up a 28$ water filter + housing on sale at Lowes that people have been using to make hop backs with. We are planning on using it as a water filter to get water in from a hose. We were thinking about hard plumbing it into the side but if we are putting filtered water in both the HLT and Kettle then something more like this would be better.
and then we could move it from one to the other without hassle.
BTW Boerderij, where can I find your sketchup models? I liked your parts diagrams you made and we are making a similar one for this project. Does the layout look correct for weldless fittings with the Compression fitting - washer - O ring - keg - O ring - washer - Nut