Bend a piece of wire in two thread it through the channel, put the paracord through the looped wire as it exits the channel and pull it back through. Alternatively just put a large zip tie through the channel and then prussic over the closed zip tie
Before buying anything I'd just hand crank it with a little thread to see if the timing is right and the feed dogs drag the fabric through. All bits are available but it's an effort to sort.
If you're planning on using the treadle (i would) you can just buy the leather by the metre and it'll...
To be fair I make down filled gear and quite often getting the high fill power downs is a nightmare, long waiting times etc. I'm been in situations where I've had a pile of unfilled quilts waiting on the down to arrive.
I prefer to make my UCR ridge-lines long so they can be used on bigger or smaller hammocks (about 10'). I make the constrictor part from about a 4' piece with a minimum 12" bury and I still need a knot or elastic band to tension it or it'll slip
Wearing extra insulation does work but it's worth remembering that the compressed insulation won't be doing much if anything to keep you warm when between you and the hammock body. Clothing augments the top quilt very well but not much underneath: you'll still need a warm enough pad or underquilt
I buy my fructose from Holland and Barret, 500g is £1.99, in the superstores they're often only periodically available.
I doubt the latest 'sugar is the new saturated fat' fad will help with its availability