Maybe you first have a look at this video for better understanding: https://www.youtube.com/watch?v=LWGVoxi … p=gAQBiAQB

A UFX lll probably has all you need.

As nice as a Digiface USB is, it doesn't have the mix of ports that gives you a solid base.
Rather than that, I would suggest getting a RayDAT (full digital card), which has besides 4x ADAT I/O:
- 2x MIDI I/O (one bus for your midi devices, the other for e.g. certain RME preamps to become remote controlled)
- 1x AES, to i.e. connect a reference converter like the ADI-2 Pro FS R BE in the future for enhancing your monitoring
- 1x SPDIF I/O
- optional word clock module as most of the preamps are lacking digital inputs and/or WC to make them to a clock slave
   the Behringer has ADAT inputs and outputs, there it is no problem, they can get clock over ADAT IN from e.g. Digiface USB
   But if you think about decades, then the Digiface USB wouldn't offer to me enough flexibility
The Behringer AD8200 used as preamp and/or ADDA converter would be 2nd choice for me
One thing is that they are really limited to single speed up to 48 kHz .. You mentioned decades, I would keep it as an option to perhaps record at double speed.
The other thing is, that I heard reports on the internet that the outputs of ADA8200 are a little noisy. But I am not sure whether this is about the older or the current model.
If I were you, I would get better Preamps, AD/DA converter if you can afford.

MADI gives you the advantage of more flexibility in cabling by supporting longer cables. If you should have more rooms in the future, you can more easily distribute devices across rooms. With MADI (via optical fiber, OM3 or OM4 multimode cable) the cables can be up to 2 km long between each of the devices! Patch cables are available between 0.5m and around 50m.

To have a device with MADI ports usually also means to have more channels in total.
This is a good thing if you need to make some trickeries with loopback.
With 2x ADAT and one MADI port, you have 16+64 = plenty of channels so that there are always some left for Loopback, without having to sacrifice other channels, that you might need for other things.

In that regard, waedi is right, suggesting the UFX III. This gives you already a good base of all the typically needed port types in a studio and in a high quality and with very fast and high-quality converters. The new UFX III has even the proven AKM converters of the ADI-2 Pro FS. So you have with it already some analog high-quality ports and preamps.
And then you have enough channels in total, giving you the flexibility for decades to grow on demand.

If you ask me whether I like AVB or Dante more than MADI .. no. MADI is a dedicated connection for Audio and this is fine.
With AVB (L2 based) and Dante (L3) you usually require switches / Routers.
Maybe you have even converged traffic, audio and the usual traffic in the house.

Then you typically require for AVB special AVB capable switches supporting all the required standards for clock distribution, which is critical. This adds a layer of complexity, that you do not want/need, and extra costs. Another disadvantage of AVB seems to be, that you cannot control sample rate across all AVB devices, you need to reconfigure each of the devices single a forum user told here in the forum.

With Dante, you have to pay for the Dante chip, require in most cases besides a router, possibly also a L3 device (Router) and you have to deal with Quality of Service. This also requires special skills, you mix different forms of traffic over your network.

Well, MADI is much easier and audio traffic is fully decoupled from the rest of the world and besides the cabling you do not have additional HW costs. Good, devices are a little pricier, but not that much and not more as if you would go AVB or Dante.

MADI has then another advantage, you can remotely control some RME preamps using MIDI over MADI with the RME connector application. And you do not need MIDI cabling for that, RME uses unused bits in the MADI protocol header for the MIDI communication, then you do not have any hassles with any MIDI cable. All can run over MADI CABLING and you have not the typical MIDI cable length restrictions.

AES has two channels and allows sample rates from single to quad speed.
But with an AES interface offering a couple of AES ports you can't connect that many stuff.

For MADI you have several options.
You mention the Ferrofish, for only a few bucks more you get the MADI version.
If you need preamps I would recommend the 12Mic from RME, this you can also nicely remote control via MIDI over MADI (all over the MADI wire) using RME connector.
An alternative would be to get a used Octamic XTC, then you can store and recall the settings using TM FX, because this device can be integrated as so called Auxdevice. Only available for the XTC though. Planned for 12Mic, but I fear this might take longer. So either XTC used or 12Mic via RME connector.