How do I know what will look best in my new house?

Ok, our house is almost built but I'm not sure about the furniture for the open plan dining, kitchen and lounge area. Here are the details so far;

Kitchen: In the middle of the dining and lounge areas. White cupboards, large 90cm silver coloured stove and exhaust in the middle of the wall with cupboards either side, long white with silver spec bench in front. (Basically 2 parallel lines of benchtops & cupboards)

Dining & Lounge: Nothing yet, just a dark grey tile (with a very slight brownish tinge) with white walls (this tile goes through the kitchen as well)

So far we have a really dark brown wood dining table and display cabinet with a tiny bit of silver detailing. We like the darker wood and the silver ties in nicely with the kitchen, however we are unsure what colours to go with in the lounge area. Should we keep it the same to have unity throughout the level, or should we mix it up a bit? Also, we were thinking of a grey (not too light but definitely not dark) coloured couch/sofa - would this work? I was hoping to add colour through cushions, curtains, etc.

Any ideas on what to do and what colours would look best would be appreciated. Thanks in advance.