Ya, its the voltage rating that is more critical than the capacitance. Even if you put a lower voltage cap in by mistake, it will just fry and smell terrible ;). Chances are, you still would'nt wreck anything.
it could just be a decoupling cap or something, and if it is, then it wouldnt matter that much. If its a filter cap, then you might "clip" the audio, but still wont hurt anything
I forsee problems running the LED and the SSR off that 30mA supply. I would just use indicators to show when the elements are on, seeing that that's all you really want to know anyway.