As long as the cap rating is the same it "should" work ok.
The "should" is there because the ESR (quality) rating may be different, which may then affect sound quality (I doubt I would notice but somebody who uses a GEq might)

You should be ok using the 50v cap in the place of a 16v one.. however it will be much bigger.

Without knowing what the 0.12uf cap does its hard to say if you can swap it for a 0.1uf one. However I would avoid doing so unless you have no choice.

Have you thought about making a PCB yourself by etching one? This might be easier and more space efficient than using breadboard.

If you are planning on more projects like this one then its well worth scavenging as many electronic components from old stuff as you can, buying new components is expensive unless you buy 100's
You can also get bags of random resistors/caps and other things on ebay for good prices if you keep an eye out.