Thank you all for your kind comments. I have so far had two clear nights of testing with the new scope and then it has been cloudy since... (of course)
My observations regarding the wire spider design is that this system is actually a lot easier to collimate than having the traditional three screws on the back of the secondary. And I really mean a lot easier! To make an all-wire design was a bit of an experiment, but I must say that I'm very positively surprised by its performance. In the past I had to loosen and tighten the screws on the secondary in order to adjust collimation and this would inevitably disturb the spider wanes. Just the mere action of loosening/tightening the screws would cause a slight rotation of the secondary from the force applied, so it was always a bit of a battle to get the mirror perfectly aligned. Not that I had to do that very often though. But with the wires I now simply turn the machine heads as required and the adjustment happens very smoothly and there is no loosening/tightening involved, it's very similar to tuning a guitar. I can adjust the secondary's angle extremely precisely with minimal effort. Also, the wires don't have to be under particularly high tension. They are definitely under less load than they would be on an actual guitar. The geometry of the wire placement is what keeps the secondary in place, and the geometry I have chosen does not allow movement or rotation in any direction.
Regarding the weight of the truss tube I'm also happy to conclude that it weighs a good deal less than my old sonotube OTA, which was surprising. But this is also in part due to the solid Parallax rings that held the sonotube, they are quite heavy! Instead I have simply bolted the dovetail plate directly to the central brace, as can be seen in the photos. I don't know the actual weights of the old and new OTA, but I will try to weigh them soon just for fun.
I found that the standard Losmandy counterweight (can't remember its weight) that comes with the mount is more than sufficient to balance the entire setup. You may notice a different white counterweight in some of the photos; this is a homemade one I made earlier because I was trying to balance the old OTA better. However, this second counterweight is no longer necessary at all and I'm going to remove it next time I'm out in the obs.
I've attached a couple of photos here which shows the parts I'm talking about.
It's looking great so far and I'll post some more details and observations as soon as I get some clear nights here.