Bending the plate to fit exact angles is very hard to do without mold or form. You might be able to roll it, but that is a really big special tool. If you have a piece of pipe the right diameter you might be able to use a cutting torch and get the whole plate glowing red at the bend area then force it over.

What do you plan on this plate doing? If you just want the look and minor scratch protection get something thin like 16-18 gauge. If you want it structural, get 1/8 or 3/16. Same goes for fastening. If you just want the look, you can glue it on. If you want it structural, weld or bolt it on with 5/16 hardware.