I read your post. You have an SV-1 and a Keystep. This rack will be in addition to those pieces.
"I want to have a lot of diversity, functionality in a small rack."
The nature of modular makes this a very difficult request to fulfill. I'm assuming that the SV-1 is going to be your go-to synth and what's in the rack will compliment the SV-1. What do you feel is missing from the SV-1/Keystep combination? Where are you going with your music?
Garfield mentioned getting the 7U version of a case. I would definitely recommend that too. It's a little more money up front. But you get more space and more features in the 7U cases.
As far as what you HAVE in the rack posted above... IF you get a 7U case, you will definitely not need the Intellijel audio I/O 1U JACKS module. Those are built into the back of the case and have a connector for the Intellijel audio I/O module.
The pedal I/O and pedal jacks I/O are nice to have. But there are better modules that will fit in that 1U space. Get an Intellijel Quadratt for mixing, inverting, and scaling your CV and even audio. You'll find it more useful than that other stuff (the Duatt doesn't offer enough channels in my opinion). Eurorack versions of reverb, delay, and bread and butter effects are nice due if they have CV inputs for real time modulation of parameters. That's something you generally can't do with most general, stand-alone effects units.
There are some things that might give you a wider palette of sound such as a module capable of ring modulation and/or distortion. You're on the right track with a wave folder. You can overdrive a signal with your Duatt... but there's no way to directly modulate the module. It's still not a bad module, though.
Another consideration is that you're using a lot of Mutable Instrument modules. There are smaller micro versions of these available. If you can handle the smaller knobs, it's a great way to save rack space for other modules.
I'd also suggest a module like Ornaments & Crime. Your Keystep has an on-board sequencer. But having a second sequencer that can be locked to the Keystep and be modulated within the rack is also helpful. Sequencers can be used to influence modulation rather than playing notes. The O_C can also generate envelopes rather than gates... so it can get you a long way even if used in a subtle manner.
To summarize. What you have here in conjunction with the SV-1 and Keystep isn't bad. Just go with a larger case. As you dive deeper into Eurorack, you're going to probably want to add more modules or swap out what you have for something else that might need more room. Give yourself room to expand.