The majority of OA i see framed is done so poorly. Here's how I generally frame mine:
Float the art on a white/off white matte (one that compliments the hue of the OA paper, but doesn't necessarily blend in perfectly). Floating is always ideal for artwork where there may be lines to the edge, margin notes, cut corners, etc. that all add to the piece and might be cutoff by a window matte.
Black mattes are a terrible idea (unless the piece itself is on black paper). Aside from being high contrast and overpowering, black is the most light absorbent, and therefor the most reflective (not to mention potentially damaging). You will be looking at more of yourself than your art.
UV glass. This is more expensive, but in theory will protect your art from light. If you don't have windows in the space, not a huge deal in the short term.
Spacers. Never let the glass touch the art. Use 1/2" to 1" inch spacers so that the art is sitting behind the glass in a shadow box style. Looks classier, and is better for the art. This is what museums and galleries do.
Frame wise, I am of the mind that less is more. I prefer depth to width when it comes to frame profile. Example attached.