Curtains, I've fitted 2 sets, in previous Vito then Viano, delivered from Germany. I see now they are available in the UK and look to be the same
These were a German brand, I think they used to be called Bauer (or similar).
MERCEDES VITO 638 V CLASS SIDE +REAR INTERIOR SUN SHADES CURTAINS SET CAR GREY | eBay
The van is improved even while curtains open. The rails need to be bent to the profile, as I fitted closer to the glass than the video shows. Use their silly little screwdriver to mount or the anodized rails can be scuffed.
I change into my dry / wetsuit often w/o curtains (not fitted to the present Vito). anyone would be hard pushed to get a flash.
We have a Kyam motor dome drive away awning that doubles the accomodation. We empty the rear into it and sleep on the floor. But I'm 'still' fitting it out with a bed that uses the rear side arm rests for support and slides forward (3 sections) to span the side doors gap. That should be somewhat warmer than the floor, which was ok for summer use anyway.
The convenience of it being a 2nd level is fairly obvious.
In truth it is a little high and it being perhaps 3" lower would be easier for getting on and off, while still allowing for storage below.
I've fitted interior tailgate LED's so the awning is lit. These are good for loading Mum in her wheelchair also. As they are wired to the interior lights I've still to fit an override so they can remain on for longer than 20 minutes if camping.
We cook in the awning with a camping stove. The pot cleaning is at onsite facilities. But that's only breakfast as other grub is invariably with pub booze.
The Vito is limited for space imo, so an inside kitchen is pushing it I feel.
Swivel seats I gave up on. I viewed that this would work for the passenger seat only as the drivers seat would need to navigate around the steering wheel. But as I have a central storage pod between seats, that gets full of many things and carries flasks for hot drinks, it is more useful than swivels.
So far I'm designing the bed to double as a table area using the removable rear captain seats to sit. They can later drop flat to support the bed that will slide forward over them.
We have a 9" Android HU (Chinese). A problem if a comand is removed is that the dash clock will no longer update, but otherwise they knock spots off Comand, and if the Vi never had Comand that's no issue anyway.
Small point but also an advantage if the Vi doesn't come with a phone pod (left of the steering wheel), 1 less obd page to pass through.
Something that is nicer is oem sunroofs, I've no experience of aftermarket. The cab just feels more airy.
If rear sunroof and fixed panel are fitted some black outs would need to be considered for sleeping, but I don't see that as being a big issue.
Maybe I can get to hear your audio upgrades some time. Comparing our Vi's could be useful.