That's not true unless you're close to a massive screen - for example, if you have a 75" TV, you need to sit closer than 10' away to be able to see an improvement in 4k vs 1080p (unless the 4k signal is better than the 1080p in other ways).
Another problem is that when programmes are streamed...
You'd need to sit quite close to one of the monster size TVs to be able to see the difference. Reading the op, 1080p (Full HD) will be just as good for the size of TVs he's looking at, but most options will just be 4k anyway.
Yep, but people imagine 4k will be better so that's what the...
Do you get any sunlight (inc reflected) on the TV? More expensive ones come with better coatings that can combat that.
You say 43" but 50" would be ok - if that's the case, I'd suggest 50" because bigger is better.
Yes, they are all proper HD.
How about audio - will you use a soundbar, or do you...