Hey Mark!
So, the H4MIDI WC (https://www.cme-pro.com/h4midi-wc-usb-host-midi-interface/) 'off the shelf' doesn't have the WIDI/Bluetooth component. I also added the optional "WIDI Core" chip (https://www.cme-pro.com/widi-core/) which turns the H4MIDI from just a physical MIDI hub into a physical+WIDI/BT hub.
BTW, if the idea of pulling apart a box and plugging in a chip sounds a bit nerve wracking, don't worry. It's a socketed chip that you quite literally just plug in.
Scott Uhl did a great video on the H4MIDI and documented the WIDI Core chip install (along with some important tips) here is case you want to see what is involved - https://www.youtube.com/watch?v=tIGvjCm2u2I&t=293s
On a sidenote, CME just released the H12MIDI Pro https://www.cme-pro.com/h12midi-pro/ but it doesn't have WIDI/BT built in which completely baffles me... you can hang a WIDI Jack off one of the outputs to add a WIDI interface, but that decision just seems messy to me, but it will work.
For the USB MIDI connection to the CQ18, yes, direct connection to the iPad and ST should 'see' it as a MIDI device via the USB is my understanding (someone using a CQ18 might want to weigh in in case I'm incorrect).
Which then leads us to the old 'how to connect all these things to the iPad' problem.
Now, there will always be some debate about the reliability of official Apple adapters vs 3rd party adapters. Problem is Apple don't have the specific multiple port config I need, so it is a moot point in this specific topic. Anyway, I'm going to park that topic entirely.
My iPad has a Lightning connector (I know you said yours is USB-C) and I've been using 3rd party adapters for years without any issues. They are cheap, so I always carry 3 of them for redundancy.
The one I use has 2 x USB-A and 1 x Lightning port which lets me connect the H4MIDI and my Behringer X32 mixer via the USB ports, and power the iPad via the Lightning port. I think this is the one I use - https://www.amazon.com.au/Certified-Lightning-Converter-Charging-Splitter/dp/B08THGX7G2
This looks like the USB-C equivalent - https://www.amazon.com.au/WASRUYI-Adapter-iPhone-Samsung-MacBook/dp/B0DPSNCMBN
Again, other folks using USB-C based iPads might be able to chime in with a specific recommendation they are using successfully. Some folks also use powered USB hubs which can provide even more flexibility. The 3 port adapter has been fine for me and I like that I can also secure everything with velcro ties when I have the iPad on a mic stand tablet holder so that that connectors aren't bearing any weight or pressure (less risk of damage in long term or having them pop out mid-gig).
Just for reference, this is my current setup:

I'm also quite risk adverse, so I have documented 'fallbacks' for individual and multiple end-point WIDI devices failing (or getting broken/lost). I also have a CME WIDI Thru6 BT in my kit bag for these 'disaster scenarios'.
So far, all of the gig/rehearsal setup issues encountered over the last 2 years have been human error:
- Me leaving BT enabled on an iPad that I had paired with the CME WIDI devices to perform configuration and updates (the BT connection will take precedence over the configured WIDI 'network').
- A guitarist (no longer on the diagram as we have let him go..), despite claiming he hadn't touched anything, had unplugged his WIDI Master from his Helix and plugged it back in the wrong way around (mixed up In and Out).
All 10 sec fixes once I worked out what the problem was.
So, touch wood, but the equipment itself is pretty reliable and dependable. That said, I hate anything made of plastic that is on or near the ground.. it is begging for a drummer or vocalist to tread on it on a crowded stage because they aren't looking where their feet are!
I would say the part of the setup that throws me the odd curve ball is the iPad and the devices connected directly to it, e.g.
- The way iOS refuses to detect things plugged into it while it isn't unlocked as a security precaution
- The way iOS enumerates USB connected devices - it sometimes gets confused/overwhelmed if multiple things are plugged in at the same time, or if they are powered on after you connect it. So I tend to be quite methodical about power up all devices before connecting the adapter to the iPad, and sometimes I have to unplug each device from the adapter, and reconnect it, just to re-trigger USB enumeration.
So, while a little annoying, I've experienced it enough times to know that it is a 20 sec fix if I encounter it.
One last point about CME - they are an amazing company to deal with and they also engage directly via the CME Facebook group. When I was first designing this MIDI/WIDI setup, I watched all the videos, but still wasn't 100% sure my design was 'right' (USB MIDI and Host concepts still throws my old-school head for a loop).
So the first version of the diagram (all done in Microsoft PowerPoint) I made I emailed through to CME. I made sure I was clear on requirements, what devices need to send/receive, etc. The CTO in Singapore replied within a few hours, having added comments to my design, confirming/answering all my assumptions and questions, etc. So I send back a revised version 2. diagram which he confirmed would meet all of my documented goals, and that gave me a confirmed shopping list. I get most of their stuff from Amazon as the prices are generally lower than most of my local suppliers and they seem to have everything in stock so I receive it same, or next, day.
Cheers,
Anthony