Hi GregSilvia / Jays,
Well about those mixers that was exactly my point, I don't understand it, so for me, if it would be my rack, it would not be okay. But for the original designer of this rack it's most probably okay. Since I haven't designed that rack, I really can't tell you why those particular mixer modules are in there.
That's exactly one of my points why you shouldn't take somebody's rack design and start with that because you/me/we just don't know what were the thoughts, the ideas and the design principles behind that to come with the rack just like that.
On the other hand there is nothing against it to use somebody's rack and take that as a starting point but I doubt if that's the road you should go. It's up to you of course but I wouldn't do it like that :-)
Please keep in mind the good advice of Lugia as well, he got a few very good points there.
Try to discover for yourself what you want and need. Did you went to a dealer and tried out a few modules, testing them, playing with them? If yes that should give you already a rough indication of where you would like to head at, if you haven't yet, I would strongly advice to go to your (future) dealer and play a bit around with a few modules. Just to get the first practice, experience and impressions and then I think it becomes already a bit easier and clearer where to go along this modular path.
Good luck and kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads