The cynical side of me says these guys really just want to sell plans. I really question if these really work.
Some warning signs for me in include the note the pvc must be reinforced with wood or a metal pipe, there are no pictures of anyone sitting on these things, and there are no pictures of details like bottom bracket and crank setup
also PVC get really brittle in the cold which we know Alberta has.
This is so far off your long stated design goals that you should just rethink them
i.e forget quad go for 3 wheel, one in back and 2 in front, forget suspension and use big tires, super light outside covering, and so on. Good luck
__________________
Life is too short not to ride the best bike you have, as much as you can
(looking for Torpado Super light frame/fork or for Raleigh International frame fork 58cm)