1a. If you hit the 3D adapter before the AVR, it does not have to be 3D Ready. If you hit an AVR with say legacy optical and bypass your avr with the video once again does not have to be 3D ready.
2. The watts per channel is sadly rather meaningless. Generally you pick a budget and just get the best you can get feature wise for the bucks.
3. Powered subs egenrall go to a line level output on the audio processor (AVR) called Sub Out.
Side ??? = Not really, most of the general population does not need external amplification to meet their needs / wants in an audio system.