Lower right. You don't neccessarily have to have all 4 feet of sofa on the rug, but you should have at least the front 2. You'tt probably want a more durable, washable rug because of it's location at the door. Best length would have to be judged based on door location and some sensible distance from TV -your 10 - 20 cm? Out of curiousity, what is the white box in the upper right of the room? Is it movable? If it is, it looks like your sofa could go on that wall, and a light chair (or 2) where sofa currently is. Then the area rug would be centred on the sofa, the chair legs might not be on it, and rug would be away from the patio door. Is that any better?

Sorry for not explaining well! Our vanity is only 75cm wide and has the door on one side and toilet too other side. Rather than having the shaving cabinet line up with the vanity (ie 75cm wide) I wanted to have the shaving cabinet run along the length of the wall (120cm) which would mean it runs behind the toilet. Would this look strange?

My preference for the width of stile and rail is 40mm minimum. I have a cabinet which has 260mm wide doors with 45mm stiles and rails. Any width less than that wouldn't look right especially if the doors are wide. I think it best to size up all the cabinet doors and drawers then do a compromise as to the best fit. Slim drawers are best left plain without the details.

As long as you balance your room (or in this case wall) you don't need wall cabinets. The wall looks somewhat unbalanced in the render but that can be easily corrected with a splash back, art, rails (such as those you get from ikea) or open shelving. Open shelves shouldn't get greasy if your range hood is working well but they do get dusty.