I have painted numerous Khornate warriors in my painting career so i know a thing or two about metalic paints xD
SO, first thing is- never mix bright metallics with very bright colours- yellow, white, unless there is clean distinction between them, like a black line or something.
For silver, it mixes well with many other colours and goes well when alone. Simply wash it with nuln oil and highlight, then you can add rust or blood splatter (which looks very nice on all silver armour).
As for bronze- i personally love it. Base of Balthasar Gold is a great start, its dark and rich, after a wash with Agrax Earthshade it can be painted with lighter bronze, or even gold, highlighted with a mix of some bronze and silver. Rule of thumb is- the darker bronze you got, the less colours mix well with it. So for very dark, lets say only Balthasar Gold, black, dark red, green or blue are good, but remember to keep them dark. And moniatures painted whole with dark gold/bronze are not looking good IMO- i have tried it several times and even with good dettail they are a bit flat. On the other hand, its a best colour to pun on standing out details and parts, like shoulderpads or weapons. About, lets say 1/3 of miniature painted with bronze will be looking really good and this will be enough to make it stand out.