I think you need to use cupboards to address the fact that the fire isn’t central on the chimney breast. Give the illusion that the chimney breast goes all the way to the window wall by putting a tall cupboard, coming slightly forward of the chimney breast. On the other side of the fireplace, maybe put some kind of slimline art, to fill that wall space. The TV could go above the fire. Possibly too put some shelves between the chimney breast and the door.

It's a lovely room. Are you buying new furniture or trying to make your existing furniture work because an L shaped sofa might work well in the space and allow for two separate zones. Also, how many people do you need seating for? Can you get away with a small dining table for every day that extends for visitors?

The mock up looks good! One word of advice to make the mock ups look as good in real life- keep the place tidy, when you first finish the decor of the rooms make sure you find a place for every toy, boom, remote control and make sure everything is kept in its place. It will make the rooms look more streamline and contemporary

clip the pipe at less than 150mm from the floor, this is the plinth height and the pipe won't be in the way when you come to fit the kitchen cabinets