Sorry for finding this question a bit late, just wanted to share my experience! I use a different monitor arm (which is carrying 2 24" monitors as well) than yours which rests on the metal beam for a bit more support. My PC is also sitting on the grill with the feet standing on the metal beam (that supports the metal mesh). I haven't had any issues so far and can share pictures if needed.
To answer your bonus question though, I'm not sure what rated weight is. My PC case by itself weighs around 7.4 kg / 16.31 lbs, so I think your PC will be fine ^^!
I think you're looking for something like this:
It can extend out to its arm max length, turn orientation and tilt up and down. Just keep in mind that with any dual monitor mount, the screens won't be able to be perfectly side by side if the arms are extended all the way out since they are mounted at the same position. I have this mount though and it seems very well built.
I use this dual arm pole mount. 1 inch thick piece of poplar mounted to the underside and grommet mounted. It can be a bit finnicky but it does the job well. Holds the weight of the ultrawide like a champ. Typically I have the top monitor just above the ultrawide. When I stream I pull it forward to game at 144hz and shorten my stream windows on the ultrawide.
i have this one and is very good and flexible.. the only difference with the one you want to pick is that with this mount you can have your monitors the one above the other too and not only in the sides. i would go for this one
Found out recently this was coming from clenching my jaw all the time. Really started working on massaging my jaw.
You might want to try dissecting a 3d model and really figuring out which muscles are the problem. For me it was the posterior scalene. No physio therapists or anyone could figure this out for some reason and if I didn't dissect this model I probably wouldn't have figured it out.
Also my set up is a 32" and 27" monitor, mounted into the air, with a keyboard tray (got rid of that tray and made my own plank about a foot long, reused the clamps and sliders), a dropdown mouse tray, and a lumbar back support