If you put your rack on public and post the link, it will appear on the forum as an interactive rack.
For a rack like this, it is common to add something like Mutable Instruments Ears or Mikrophonie right at the front. It boosts the signal to Eurorack levels. It's essentially your output module, but in reverse. Things like filters and distortions react differently to different gain levels. Both of these are not in stereo though.
Alternatively, VCAs with extra gain (i.g. Mutable Instruments Veils) can also boost the signal to the right level for both L and R signals. The advantage of the first method is that you also get a gate, envelope follower and a piezo microphone. The envelope follower will work nicely with the Nebulae. The raw piezo noise works surprisingly well with tons of reverb and effects.
If you're not going to record with the in L & R from the Nebulae, but will only put samples on the USB stick, you can skip the above contemplations.
Behringer is obviously hideous and shite, but you don't need me to tell you that. I always mention ARC by NANO and Rampage by Befaco as affordable Maths equivalents.
I wonder if Zverb and FX Aid will play too much in the same ball park. Zverb is also mono in, while the rest of your current setup is stereo.
A mult could be good, but in your case I think two small stackable cables would suffice. You can stack on both ends, so it's essentially 1 signal into 3. It's cheaper and you don't lose the (soon to be very limited ;) ) HP space.
plaits? qu-bit chord2
I don't think Chord has an use case in your system. It will be similar to the samples you recorded in your other synths or DAW or on the Nebulae. If you record some chords on your usual synth, you have total freedom and complexity. All of the notes you play on a synth have their own timing, envelopes, individual filter movement. Chord just outputs a set of notes without all that (im)perfection. I'm not sure what your further synth setup looks like, but have you considered a Moog Mavis or Mother32 or Labyrinth as a future sound source? You have the space on the second row. Plaits, as you mention, is also a popular choice.
XAOC Zadar could be good, it has very complex envelopes/LFOs. There's many shapes, but it's a set library though, some people don't like that.
If you have a friend with a 3D printer, they could print you some blank plates, to hide that empty second row. It's a little safer and nicer to look at.