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?

I don't know about it , can you change it, you can have modern and different but I think your tv unit is mid century style and table is Well I don't know what style it is than you say you want tribal . As someone suggested earlier , stop shopping before you move in it might be all wrong and your taste and ideas might change by then. Trick in decorating is to be patient and only buy when you are absolutely sure that you can take it back. Ha ha.

What is the difference between an Oriental rug and a Persian rug?

Why have you quoted all sizes in feet and inches. We have been using metric in Victoria and Australia since 1974.