I'm a complete modular newbie and so your comments and/or suggestions are very welcome!

My current system consists of a Moog DFAM, Subharmonicon, Roland TR8-S and Eventide H9 Max.

What exactly are you trying to accomplish music-wise. All of the racks you've put together and posted are very different. Also, the QMMG pictured here is long discontinued, so you will pay a considerable price for one.
How much research have you put into the functions of each of the modules in your multiple racks?

I think there are nice options in there, but it is not cheap, most modules are a bit expensive in my eyes.

You have not explained what you want to do, but for most purposes you need a output module mostly with a mixer.
To stay in the Make Noise modules, the Rosie is not a bad choice for most purposes as output module.
Only if you want full stereo paths (not all the modules you put in here are stereo), then the Rosie is not the best choice, unles you use the X-PAN (also make noise) as mixer and link the outputs to the Rosie's return inputs.
The X-PAN also pairs well with the Dynamix (not produced anymore) or Optomix, and some other modules for decentral mixing.

I use the Rosie (mono path / stereo output) with the Pico DSP (an Erica Synths module, not a make noise module).
For both channels of the Rosie I have a mixer (cheap, slim and modern Doepfer) and a VCA.

I hope this works :
ModularGrid Rack

Thank you for your comments.

I don't have very specific goals in mind. I listen to experimental techno and house but I'm not particularly concerned with making polished, stand-alone tracks, at least for the moment.

I want to put together a system that allows me lots of opportunities for exploring sounds, patterns and rhythms.

I was wondering about output. I have a Allen and Heath ZEDi 10 mixer. I can't just route a signal from any general output then?

Modular signals are much hotter than line level, but you can usually get by without a line level output module. I plug directly into my mixer, but just keep an eye on the gain.
You have posted many different ideas for racks in this forum, some of which might be fun and some definitely won't be any fun at all. I would recommend looking beyond brand name and matching panels to find different modules that will help you accomplish what you want. A Make Noise Telharmonic is going to sound vastly different from an Intellijel Dixie or a Mutable Plaits, and you will need to consider what utilities might help you achieve the sounds you are looking for. Why would you need a modular over software or other hardware synths? What is the benefit of pursuing your music this way?
I would recommend checking out VCV Rack to make sure you have a good handle on what is necessary to make a modular synth work.
Have fun and good luck!

Thanks for taking the time to look over what I've been putting together here and give your feedback. It's much appreciated.

I understand the need to look beyond big name brands and mix things up a bit.

Partly that was to keep things simple for myself as my knowledge and understanding developed.

Partly that was because I thought modules from bigger names would play more nicely for a newbie.

I will definitely be taking the plunge soon. I can't wait!