Grantmac

I'd not spend the money on an Inon viewfinder, the Nauticam units are far better. You can use the older DSLR style on most mirror less with just a little corner distortion.

I would skip the mini flash, getting it to work was a pain for me. I'd look at one of these: https://underwaterlightandmagic.co.uk/

There are two ports that the sync cable can plug into on that strobe, which are you using?

To figure out flange distance I'd compare macro port length, not extension for domes. Just because companies seem to make different dome geometries for the same lenses.

I have access to a chamber which can do 100m, but it's in Victoria BC.

It doesn't exist on their website so....

I see extensions which allowed Nauticam N120 to be used on a Marelux housing, but nothing for the other way round.

I wonder if you could rig some sort of non contact switch like a magnetic reed switch? I've considered that for the vacuum alarm so I can keep it sealed without killing batteries

Of note this is not present on the a7iii housing. So likely was a good idea that didn't work too well. I wish that I could do eye detection for the EVF because the I could easily use the LCD for settings like on a traditional DSLR

I see extension rings for using Nauticam ports on Marelux housings, is there a forthcoming extension for doing the opposite?

Another option other members have been happy with is the Howshot 140mm, about half the price of Nauticam.

I have the n100 to n120, I just wasn't sure if it would be too much extension by the time you add the n120 to Marelux adapter

There will be an N100 adapter eventually?

Anything threaded gets attention daily. Ports stay on until changed. Main oring gets inspected and cleaned perhaps monthly unless looking sandy.

You might look at the wireless protocol used by Halcyon for their new CCR controllers. They seem to have both range and bandwidth. Likely proprietary and expensive however.