Don't Apollo Blinds do every kind? Cleaning blinds is a horrible task. They sell some crazy looking brushes for that task but i have not tried one.

Well...not exactly like that one, but close. Mine has a lever handle built into the larger handle, so after unlocking it we operate the lever to open the door. The one you show looks like it unlocks, then you simply push the door open. Is that right? Here's a photo (exterior and interior) of mine.

Yes, I do think it would pick up the retaining walls. Which I don't know if you think is a good or bad thing! I think the shale grey will come out a bit lighter, but it would be harmonious with the yellow brick and with the retaining wall. Are you keeping the ironwork? It's an interesting feature. Perhaps the fascia is better left white if the ironwork is remaining white.

What performance is more applicable for your climate? Double glazing will perform significantly better than single glazed whatever in regards to heat loss. You can't beat the air gap factor if you're trying to keep avoid heat loss. Yes there are "Low E" single glazed products such as viridian Comfort Plus which depending upon which side of the glass the absorption coating is placed it will perform in different ways, but bear in mind that since it also will reduce heat gain in winter it can actually work against passive solar building performance if not properly applied. In other words, it's not a "cheap" replacement for double glazing. In Victoria, we generally spec standard double glazing and use external controls such as blinds to mitigate heat gain issues in summer. Thermal Performance Specialists such as an Energy Raters understand the technical nitty gritty around this issue the best, and always good to seek their expert advice when applicable.