I want to use faux blinds but not sure which way I want to go as far as the sizes. Unless I get an expensive custom, I'll have to get at least 2 blinds.

Would you
1. Purchase 2 blinds and have to open up a 4' blind to allow a free flowing breeze.
2. Purchase 3 blinds (2', 4', 2') and only up the ends and keep the blaring south sun out but allow air flow.
3. Go custom

Option 1 I'm concerned it may look funny and point out that I was too cheap to purchase a custom 8' blind.

Option 2 MAY look more purposeful having blinds specific for the operable ends of the windows.

Option 3, could get very expensive for a room rarely used and the window itself may need replacing due to its poor quality. Even though custom, I'm concerned about the mechanism failing when the blind is adjusted up and down over the years. It's been awhile since I checked and most didn't guarantee the blind when it got that wide.

Background info...We need a window covering for privacy mostly. This room is mostly used for guests. Since the view to the outside is just the street view, I like the idea of blinds to diffuse the lack of view.

If the 2-4-2 is less expensive than the 8', and you need maximum privacy yet allow some air thru the room, then the 2-4-2 would be a better option. I would not raise and lower the 2' sections, just open the slats for air flow.

If you choose to go with the 8' I don't think you'd ever want to raise and lower it. Again, just open the slats when you want air flow.

If you go with the 2-4-2, I think you want to order them hung on the same header. That way you'll know they'll always hang straight and evenly.
As for replacing the window......a new window in the future shouldn't affect any blinds you buy now. The actual window opening wouldn't change.