When I cut out old stuff to replace with a patch panel I outlined the patch with a sharpie than on the frist cut ,cut it maybe a 1/2 inch below the line , one trick is to get the patch to fit tighter and have a closer fit so you want to make the final cut "mark" as close to the new panel fit as it will be when your done .
that cut off wheel is fine
Practice is the key and common scense
Pete
