The wood is less then 1/4", then there's 1/2" foam padding and vinyl.
They're just held up with velcro for now but I'll be adding some button tuck details around the edges to firmly secure the panels and add some style.
Looking at your pics, what I think I'm going to do is just get a 3/8" plywood board, use my current panels as templates on where to trim it down, and then mount it on the metal ribs. I'll glue the vinyl upholstery over that and tuck the rough edges in enough so they won't show. That way the wall is sturdy enough, but will still not be too tall where the window trim won't meet it.
I should be able to screw in lights, speakers, and whatever else I need to them without risking the 5mm or 1/4" wood not being able to support it. Plus I should be able to get enough of a curve going.