Hi, it's difficult to provide suggestions without seeing the color and style of your living room. Are you looking for traditional or contemporary feel?

Without seeing it nor the colour on your walls (which also plays a part), I would say you could take any one of the colours from your carpet as your colour for the upholstery. Yes you can choose two complementary colours for your upholstery but make sure they work tonally. (To do this take a picture of the colours and render them black and white; the colours for your upholstery - even if they are different - should have the same level of grey in the b&w photo).

Probably the same material as the kitchen and rest of the main floor.

If you have a small living room go for white/ cream/ beige curtains to make it light and bright. If you have a large living room go for a darker shade like a mocha grey/ brown for curtains to make it warm and cozy.