I can give you specific suggestions, though I hope you'll also keep looking at other stuff to make it your own.
Sample and Hold: Divkid RND STEP is a good one that offers a lot of function in a small amount of space. You can easily just get the 2hp one as well - this doesn't need to be a complicated circuit to be cool - but then you always need outside modulation.
Envelope/Function Generator: Most of my favorite modules like this are big (Buchla 281t, Maths, Doepfer A-143-1 and 143-2). If you can spare the space, modules like this can make your system really come alive. However, Vostok (the Atlas company) makes an envelope generator that is smaller but gives you tons of loopable envelopes for modulation.
VCA/Attenuators: This is a category where you should do your own research and find out what works best. However, the various clones of Mutable Veils, such as After Later Audio's Cloaks, are popular and have lots of options. I have a Frap Tools 321, an attenuverter, which is very different but works great for me. Learning the differences between these two will help you better understand what works best, but they're both well-liked and popular, and that reliability is a good sign you can use them to learn about this stuff.
Multiple: Definitely get a mult or two. If you want to multiply audio or pitch CV, get a buffered mult (whichever's most popular). If you don't want to do that - and with this many oscillators, I don't know if you would - I'd just say look at 0hp options like the Qu-bit Splitter or the Intellijel Hub. Cheap and easy.
You have a lot of effects in this rack. It is nice to have effects that talk to your modular stuff, but it does take up space for stuff that can be done outside the rack pretty easily. I do think the Versio modules are interesting because of all the different firmwares, though, and keeping one (or both if you're set on them) might be a good way to explore a lot of stuff in one module.
Honestly, you may also want to think about something like a 1010 Music Bluebox standalone (or another mixer that can handle eurorack levels as well). You're going to have a hard time getting a module in that rack to handle 7 audio sources gracefully and ergonomically (especially for techno, where you'll be happier if you can mute stuff and do effects sends). Plus it frees up your Doepfer Quad VCA for more experimental purposes. I don't really understand the way you have it currently with separate mixers for drums and oscillators and then a single stereo out. If you have a reason for it being that way, then that's different, of course, but I think mixing is just one of those things that's hard to do in the rack without a whole new row for this stuff.
I don't know how you like to play this stuff, so you may choose modules that have different sizes or interfaces to these ones to highlight what you like more. Even that big Vermona module could be very useful if you thought you'd get a lot out of having big luxurious knobs and lots of space/options for your LFOs - it just depends on where you want your hands to spend the most time and what parts of your music you want to have control over in the moment. These suggestions are just me trying to add simple functions to what you already have and not change your original vision too much.