You need to make a decision. Do you want the fabric to bring colour and pattern to your room or do you want to keep the whole room neutral? If you want pattern, the next decision is what style- check or plaid, stripe, floral or geometric? Then what colour(s). The room, as you point out, is not overly bright, but do you use this room much during the day or is it an evening room? You could opt for deep, rich colour that warms the room at night like burgundy, deep turquoise or terracotta. Adding patterned cushions with similar colours will splash colour around the room. Also, I'd replace the Roman blinds with matching fabric to the curtains, otherwise that will will lack colour. You could make a single curtain for each of those smaller windows in your main fabric and pull it to the side furthest from the fireplace, tied back. As to style, since you don't appear to be overlooked, floor length curtains on the front window and patio doors can be on a 50mm pole extending at least 150mm plus finials each of the windows. To stack them further back extend the pole more, but take care not to have wall showing just before the window recess. Tieing them back would allow more light to come in. Check out readymade by Montgomery https://www.montgomery.co.uk/ready-made-curtains/whitworth-21-duck-egg/9927, John Lewis (Scion Navaho), Terry's Curtains, Heals. If you choose a multi coloured pattern, later changes to your lounge will not necessarily mean that you need to change the curtains. Remember that decorating your home is less about style and more about you and your family. Have fun.

I think pale curtains to match your walls, or near enough, would look good. I find dark curtains depressing, especially when they’re closed. I would introduce more colour with artwork, but the restful pale grey is great and is very stylish, so I think colour should be subtle like a soft blue or teal or blush pink. Such a lovely room.

In my opinion it depends on budget. The best option is to take off the wood cladding and coving and then get a plasterer in. The budget option is to sugar soap these walls to ensure there is no wallpaper paste residue, then fill and sand any cracks and also use decorators calk to fill cracks in corners and next to woodwork. Then you need to mist coat the walls which is basically a watered down coat of paint. When that is dry it will need two rollered coats of emulsion (3 if it’s a strong colour). A very flat Matt paint shows imperfections least. After the first coat of paint check it for any bits that might need more filling. In conclusion the key to a nice finish on the walls is lots of preparation and then a low/ no sheen paint.

So Skimming Stone is very close to Ammonite in terms of Value (lightness) but it is more colourful than Ammonite, as it has a bump more Chroma. Increase in Chroma can help towards combating gloominess in a space. Lower Chroma colours are much more influenced by the changes in light. Pointing is the lightest of all the colours you have mentioned, but sits in between both Ammonite & Skimming Stone in terms of Chroma. That quantity of Chroma is still likely to help keep the trim looking crisp as the skirting is likely to have less Chroma. Because of it’s location on the Color Wheel & the fact it has low Chroma, there is a chance it might shift blue in imbalanced light. It doesn’t mean it will happen in your space, but it may. So again, testing on moveable lining paper is helpful. It’s in those dimmer spots where colour shift may happen.