Honestly on the the 3 design elements :
1 - Copper / Brass thumbtack on the grill way too "1962" trust me. Plus it does not go with your flow using carbon fiber legs at all. Your adding work, and calling attention to something that honestly makes it look more "Garage" built in my opinion.
2 - I am not 100% sure if these are planned for real world production or simply a concept for maybe providing flat packs or something, however you can get grill frames punched out 20 at a time from single sheets of whatever .25" material you want with all the beveling, cross bracing etc... on a CNC machine for probably 20 bucks a pair which would save you a ton of time, materials, and money unless you love the self inflicted pain doing details like this!
It's a grill so I see it as 100% industrial function for protection so I would never listen with them anyway.
By the way I do know of a mass production place super professional that can do the grill frames with state of the art CNC for any possible design you want punched out, and they will do pretty small quantities, with magnets, and all installed already, and yes they are easy to talk to, and located in the U.S. I think they will even put the fabric as a finished product, but that would cost more obviously.
3 - The leg concept is interesting, and I get going for the "Design" element of it, but I will make a serious suggestion here. First you are putting a ton of stress on those bolts holding it to the cabinet regardless of the clamp mechanism, so if somebody tilts this thing, or pulls its weight across the floor I think you risk some type of cracking, or damage at a point in the future. I would highly suggest simply cutting out full "Outriggers" that cross the bottom of the entire cabinet either from metal, or even wood could work, and this will take all the stress off, and give you plenty of surface area to bolt, and place wherever you like into the the speaker. Gravity will do the rest. And then use the "Legs" attached the to the top of the outrigger simply as an ornament with a single fancy clamp you came up with just for audio jewelry to give the design element your looking for, and ultimately save a ton of assembly time.
Then you don't need to try and get the shear strength of bolts like the M3 you mentioned, or anything into the tube itself for alignment, and keeping it from slipping, you just put your tube thru the clamp tighten up so it looks cool, but really has no a critical function at least that your battling with. Otherwise your putting a lot of bank on those tubes to do it all, with clamps holding a heavy speaker in the lateral plain basically "Floating". Again this can be eliminated with a simple cheap, and very effective fix using outriggers like in the photo to pull it off, and you never have to worry about the engineering on this part. Plus it still looks just as cool, and maybe even more robust than before.
Yes I have built many speakers