burgundy is somewhat of a neutral color so you could get away with wearing either pair of trousers (I love how English people say "trousers" its so cute!). the mustard chinos would give you a more edgy daring look, and the gray ones are a bit more safe. whatever you feel like doing is cool. I'd tell you to wear brown shoes with them
i'd advise you to wear a plaid button up shirt under it like dark blue that has some burgundy in it
I love the look of both the "trousers." lol And I do agree with prettybrown when she says the grey is safe, while the yellow is more edgy. You could pair the cardigan with a collared shirt and one of the shoes in the Casual section of that site.
First off, I love that burgundy color of the cardigan! It looks so rich with the color of the pants! You could wear a navy, green, or white shirt with it. Don't overthink it! Fashion is supposed to be fun and comfy! :D