You can foreshorten the hall with a striped rug. Add bright colors like this and who'll care about how long it is? The unity of the black frames might make for a great gallery grouping. Cut out the shapes of all your pictures in butcher paper and lay them out on the floor to plan a grouping. Then tape the to the wall where you want them to see how they'll feel. If the grouping is the right size, you might mount a floating shelf under them. That will keep the floor clear but will anchor the decor wall.

Sorry, maybe taken back by reading all the comments, but I see that the coffee table is wooden, with the dark flooring and the lounges being a dark red, definitely you need to put a rug under the coffee table to lighten it up with a pattern including some beige or maybe a bit of mustard with red or brighter blue like on the chair around the dining table. It appears there's a mixture of older style lounge and coffee table compared to the white plant stands, something to think about as in the look you are going for.

Timber with timber can work brilliantly, and it's in keeping with the mid century style you want for your home. This room (below) is a little similar to yours, albeit with less of a pitch to the roof - the large feature lighting helps to break up the expanse of timber on the ceiling. You have a lovely open plan area, so I'd be inclined to use rugs to create zones and a cosy feel. Rugs reduce the impact of a large expanse of flooring material. They have the benefit that you can swap things around to change the look and layout at little cost. I think one trick may be to define your "walls" carefully, and paint these before you go with a new floor. This should give you a sense of whether the timber is overwhelming, and how to balance it. E.g. You might decide it works best to paint the kitchen cupboards to white, to give you a more seamless look and work with your new counter tops. If you want to experiment with the "paint ceiling" approach - gulp, it's a big one!! - then maybe that small section above the kitchen bench, at a different angle to the rest of the roof, could be the spot. It seems to have the same horizontal line as the wall, so even if you don't like the painted look for the whole, you might be able to get away with blending this into the walls. Best of luck!

Yes painting is not a task I enjoy & think the concrete is probably best left as is - with the exception of a good wash.... that being said .... I can almost visualise the building now with black/charcoal windows & doors & lots of mass plantings creeping up to the concrete & now feel the dark growth on the concrete might just serve to pull the space together with the help of a structure overhead. Hahaha listen to me... I've gone from hating my concrete to almost defending it :) Siriuskey could you try posting the link again please as it just goes to Google home page? Or even a search topic & I'll try to find it. Thank you all for your suggestions & hopefully I'll have an updated image to share sooner rather than later.