Five channel amp setup help - Parasound A51

I just picked up a gently used A51. I think my excitement about the unit overcame my best judgment, and so now I have some questions I wish I had answered beforehand. But any help you guys can provide would be helpful:

1) The unit is placed inside a wooden media center. (Pottery barn Logan medium to be precise). It has 3 inches of air space on either side, but only an inch and a half of air space above it. The back of the cabinet has a cubby hole for wires - so basically no outlet for air through the back at all. The front is open - no doors. Has anyone used an amp such as this in this type of setup? I'm afraid it will overheat very quickly. I can take off the wood paneling in the rear of the amp for better airflow, but I wonder if even that will be sufficient.
2) I am using Sonance 831s for the ceiling surrounds. My home builder installed 14 gage symphony audio wire that goes from the amp to a volume control buried in the wall, which is set to max, to the speakers in the ceiling - I am guessing a total length of 30 to 50 feet. Is this gage of wire OK given this amp can output 250 watts of power or up to 60 amps of current per channel? Or am I at risk of starting a fire? Also, given the amp is capable of outputting 250w and the Sonance are rated to a max of 100w, am I in danger of blowing out the speakers even if i attenuate the signal coming out of my av7005 marantz preamp?

As you guys can tell, I'm new to the home theater setup so your patience is appreciated. I had an A21 before for my stereo setup but that was placed on the floor with nothing around it (I was unmarried at the time) and so heat was never a problem.

Thanks in advance and looking forward to reading your advice.