You have a mixed colour palette & an eclectic range of furniture which means that you will end up with a very interesting room indeed. First suggestion: reposition rug so that all of the sofa sits on it equidistantly. At the moment your main colours are: chocolate; white; tan and grey from your sofa, entertainment unit, dining table, kitchen etc. These colours always look great together particularly if they are teamed up with black. So I think if you choose the right artwork with these colours; add copper items to top of your tables and choose cushions in these tones the whole room will come together. You will successfully mix old and new & it won’t be too bold for your taste. Note: artwork should be purchased first & be landscape in orientation. Could your existing artwork hang in the kitchen or hallway as it would be seen from the main room? To give you an idea of what I mean see pic below. Not suggesting that these items are what you would personally choose but focus on the colours and how everything is tied together. PS you could put some of your ornaments on the coffee table.

Hi Fivedock If you're using a tile that looks like timber I think you would be best using the same tile from the front entry throughout. However if you used a tile that looked like stone or concrete in the kitchen/ back area for example, you could possibly use another that looked like timber in the front entry/ living room with fireplace. Or vice versa. This only works because you have a contrast between stone and timber and there's a reasonable demarcation between the living room with the fireplace and the back area. It looks terrible if you have two different timber tiles or two different stone tiles.

all heaters and stoves should have very specific installation instructions including distance above the stove to any mantlepiece and i suggest you start with advice from local suppliers and then confirm with specific written instructions from each manufacturer that you can usually find on line...There are a number of heaters that have wood fires that are designed to be inbuilt in a purpose made wooden frame so hopefully this can be done inside your opening

This looks like a type of timber veneer, quite popular back in the day.