Looks like it will hold the Plasma with no problem. The only comment I would make is to make sure that the frame is actually attached to the studs behind the drywall in the nook. You will be hanging that nice tv on the front and it would not be a good thing to have the entire frame slide out of the nook because the tv accidently got knocked or pushed.
We don't use it very much, but I think it would be fine. It vents most of the heat out the back of the fireplace to the outside. The next time I fire it up I will check the temperature near the plasma.
do you happen to have the specifics of how you constructed that frame? i know the width will depend on the size of the nook but i was curious about te rest of it. im having the same issue except mine is over the fireplace in the corner of a room and im debating on widening the nook or framing or just covering it up all together. thanks!