Need your advice about custom maxx chassis braces

It could be strong enough, depending on the design, but that material is not thick enough to screw through to attach the braces to the chassis, transmission, and skids. Unless you find another way to attach them to those components it won't work. If you need a source for thicker 7075 plate there's www.OnlineMetals.com and www.SpeedyMetals.com

Edit: Just to add to what I was saying, you probably want at least 6mm thick plate, as some of the holes are 3mm, leaving 1.5mm at minimum for each side.