the "cotton" side goes towards the metal so that the rubber backing faces you. The original one was held on with plastic "T" push pin fasteners, is there a reason you want to glue it in? Are you smoothing your firewall?Or are you just applyinga "tack" coat to help hold it in place?
As to additional sound deadener, it depends on what your overall goal is.
Basically it's weight versus quietness. If it were me, I'd do one or the other, unless I wanted limo quietness. In which case I'd buy a Lincoln Town Car.

Good luck with it!
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Scott Heath
http://www.cardomain.com/ride/2400202

New year, new projects...