Haha thanks!
I was thinking of 4mm carbon - or 3.5 for slightly more flex, but 4mm seems the standard for durable towers
The turnbuckle mounts will be 3D printed - at first anyway. Even though I'm pretty confident the 3D printed nylon will hold - unless maybe it is crushed on a hard trackside object (poles, edges of barriers, etc). I've also made suspension blocks and hubs from the material that held just fine.
I'll order one or two plates for myself soon, plus 1-2 pairs of blocks/mounts - I hope to be able to test it in 3-4 weeks time. If there are no major issues I'll put it on sale a.s.a.p