I have confess I got a little lost in your question, but I can offer my advice. I try to have the least number of blinds as possible, of course the blinds need to fit into the manufacturers size tolerences and some common sense comes into play too. If you need multiple blinds across a very large window and want to avoid multiple chains to operate the blinds, motorization is always an option (hard wired or battery operated). For stacking slider doors, I usually have a smaller blind over the main door opening and a larger blind over the balance (as I find the smaller door opening is used more frequently, and access is better this way). I prefer having the blinds meet over the windows mullions (rather then over the glass) to offer the most privacy possible as the blinds will have a gap between them. I hope this helps you.

I am a big fan for plantation shutters you will be excited you did! You will make your money back & ease of re sale as people want them .Otherwise... If not With your kitchen get a professional in and get a tint on your window you can see out but they cannot see in until night then a simple blind will suffice. Lounge rm attach to ceiling!!.. to floor sheer curtains with a good colour curtain behind going the whole width of the wall.. bedroom a Roman blind... take advantage of your floor boards and do it properly the first time and save money!

I like the blue touches already in the room, which reflect the brickwork. Agree with lots of creams/ neutrals, just adding some blue in cushions, artwork. Maybe a bluish/cream rug, with a subtle pattern, not a solid color. Also I think the lights are a little lost. The high ceilings could take some quite large shades, maybe drums. And I agree that the central column could be painted to become the focal point as stated. Either white or quite a dark grey/ blue, ( it might darken up things too much, but it's only paint, can be changed). It might be sinful but I think I would replace it with plaster, then paint it. Finally maybe a dash of 60s burnt orange or mustard if you want to want to keep the retro theme.

Yes, the steps are a small challenge. My suggestion is to work with that angle of the steps. If you would like full block out curtains, angle the hem of the curtains with the steps. With the width of the opening, and having the curtains pull to each side from the middle, there will be quite a bit of bunching. So I would suggest one curtain fitted across left hand window. Then the remainder of curtains pull from the door opening panel, back to the right. Depending on our much 'block out ' you require, I think the following product from luxaflex looks your style, but would not bunch up on the sides as much as traditional curtains. https://www.luxaflex.com.au/products/blinds/lumishade/ Still working with the angle on the steps.