Ummm...I really don't mean to poop in your cherrios, I promise we are trying to help not razz you but......Atilsley wrote: I'll build three or four sturdy wall brackets, plus ceiling supports. Studs I wall are metal frame, so sturdy. I will also be building a ply decorative front panel to cover the whole job.
In my line of work I see a lot of metal framing, EVERY time there is a known location for cabinets or even TV mounts (a lot lighter than what you got) there is wooden backing put in. Metal studs are great for framing, not so much for mounting stuff to, screws strip extremely easy. Is there a anything behind that wall? If it is fairly open you could drive lags through the wall into wood 2x4s on the far side or all thread and bolts. If that isn't an option you may want to cut out the drywall and add some 2x6+ backers, may be a mess but you should need a nice patch job and it is way better than crushing your gear or persons with a THT. I personally wouldn't trust hanging a tuba from metal studs, even if you use EZ anchors or toggles it will be sketchy at best.