1. Yup, Quantum Pro not only has a Loctite steer tube into the headset, the steertube is also proprietary size:
1-1/16" Changing the fork is not really an option, but it is a damn good fork. I've been riding mine for 15 years with no headset or fork maintenance required.

2. The tubing they put in the internal cable slots of the bare frames are just guides to get the cables through - slide cable in, slide guide out. The top tube brake cable path has stops on both ends, the shifter cable paths have ferrules on the top and open holes near the BB.

3. BB on Quantum Pro is plain old English threaded 68mm.

4. I always had the rattle on rough roads too, but I had a bike shop do my re-cabling for the first time last month and the rattle is now magically gone. I don't know if they used a liner inside or not, they used the Jagwire Pro set I brought in to do the job and that does come with a "slick lube" liner.