Yes, as I said all utimately feasible.
Powered speakers - check out computer monitor speakers, I have an old pair of Gateway speakers for example that sound very nice.
Controlling turntable - runs off 120V? Most straightforward way might just be a relay that the uC turns on/off via transistor. Do you need it to end in same spot? Put an optical sensor somewhere, magnetic switch, stop the motor when it comes around.
Pressure pad - still thinking about that.
Cable choice can be made to work.
Distances seem a little funny, but can be sized to suit. Is the bench backed up against the case, or away from it so one can see the case?
Lamp - this kind of thing?http://www.ikea.com/us/en/catalog/products/70172578
Looks to have separate power supply, can put a transistor in the 12V return line & use that to fade the light.