Re: Frameing Mirror
What you use depends on the look you're going for. I framed a bathroom mirror about the same size with colonial door casing. You can use chair rail or crown as well, again, depending on the look you're going for. I would suggest finding a door and moulding shop that has a nice selection of trim styles.
When I used the colonial casing, I cut a rabbet on the back of the narrow edge, then cut it to fit the mirror. The casing was nailed directly into the studs in the wall. The bottom piece was rested on the counter top and nailed, the mirror then set in place, then the top and sides were installed, securing the mirror to the wall. I painted the trim before installation so that all I'd have to do is touch up the nail holes once it was installed. A word of warning here, mirrors are reflective, so they're going to reflect the back of any molding that partially covers their surface. To "hide" this, you must paint/stain the back edges as well as the face. The same would apply if using crown or other moldings.
If you intend to hang the mirror by the frame, then you'll have to make the frame structural enough to handle the weight. I would suggest you go shopping for large art or framed mirrors and see how those frames are built and hangers attached. I could describe that here, but a great deal will be lost in translation, especially if you are unfamiliar with woodworking techniques.
Good luck and report back with your progress.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!