#2
The amp will be putting out 100W no matter what if all is well.

that power will be distributed to the 2 cabs evenly providing they are of the same impedance so you're going to be hearing 50W from each cab
#4
well you'd have more speaker distribution. It might be perceptively louder, but not really much.
Ibanez -> Peavey -> Eardrums

Apparently I'm on some list of people to listen to..?
#5
it'll sound "fuller" because the sound is being projected around and more air is being moving (instead of less air moving more with just one cabinet)