Dryhopphing will impart mostly aroma to any beer and you are correct, long term storage of beer will degrade the hop. The first to go are the most volatile (aroma), the last to go is the the least volatile (bittering). Personally, I would not spend the time or money dry hopping any beer that I...
I have bulk aged many meads with head space with no problems at all, you will not have the same oxygenation problems with mead as you would with wine or beer.
Sounds like you under pitched your yeast. For a really high gravity, you should be at around 400 billion cells. I have learned my lesson the hard way on this point.
The only difference is the post configuration for the CO2 connection and the draft line. Pin lock has pins that connect with a push/turn of the connector and ball lock has ball bearings that retract with a spring loaded ferrule. One is not superior to the other but the big difference is...