Create circuit for 12v auto washer pump to 230v mains with push button for art installation
Is my circuit design correct? Are all the cables connected to the right terminals?


Yes.


  Are these component examples adapted to my usage?


The breaker won't do anything.  If it's a modern supply, it'll do its own current limiting; if its an older supply it'll burn up long before the current gets to 50A.  A 15A breaker would be more appropriate, if you don't trust the supply to limit current.


  Can a higher voltage rated switch be used in a 12v circuit, all else being equal?


Yes.  For the most part, switch voltage (and current) ratings are maximum, not minimum.


  Can I power two systems (the pump and the LED power for the illuminated switch from the same breaker or do I need an additional fuse?


One breaker will do.  The rule for a protected circuit is that all the wiring is heavy enough to carry the current that the breaker is rated for, or that the wire is inside an enclosure that'll contain the ensuing fire.  It sounds like you'll be satisfying both of those rules of thumb.