The reason for moving the Strega is because it has its own cab and power, and the Eurorack cab is for things (as a rule) that DON'T have those. So here, you're taking up a healthy chunk of hp for that, which now blocks adding modules.
The better solution would be to remove the Strega, then fill the space left with modules that can expand BOTH the Eurorack cab and the Strega, since there's no bar against patches that go "outside" of the case.
Plus, check what's NOT in the case due to the Strega. For example, modulars need VCAs...but all you've got of those here are the ones in the Strega. Not good. So take 8-12 hp for some proper VCAs right off the bat. No attenuverters, only one (DC-coupled) mixer with a mono output while there's piles of stereo path modules, and so on. Part of that can also be fixed by looking at SMALLER modules with the same functionality. For example, the Starlab. It takes up 28 hp, costs $650. So, instead of that, you could go with a Rings clone and a basic stereo reverb such as Purrtronix's spring reverb clone. For the Rings clone, my suggestion would be Oscillosaurus's version. Those two together fit in 22 hp (you get 6 back) and cost $304-ish. That's less than HALF of the Starlab's cost, and it replicates much of the primary functions that the Starlab has. The rest of the stuff, such as LFOs, etc, are already supposed to be in the build already for other functions...which, again, you're crowded out of having in here. And yes, I AM counting the Maths that's there, because using it just as an LFO is like buying a vintage Lamborghini Countach and just driving it to the grocery store.
...and so on. Fact is, there's NO ONE on here that can precisely nail a build on the very first try. The process of building one of these instruments requires a pile of thought and constant reconsiderations to arrive at a system that both fulfills your needs AND which has the necessary module complement to be an instrument that you'll use and grow with over years, instead of a noisemaker that'll wind up in a closet several months down the road. Plus, you also find ways to make it cheaper, like the above strategy. And even though I've done loads of builds on here for others that I can knock out pretty quickly, I'm doing that with 40+ years in electronic music to inform me as to how they should be built out. I might SEEM fast at that, but if you factor in that backlog of experience, you eventually realize that you have to factor the experience into the time outlay. Others on here also have similar background experience, and can do much the same thing...but it's due to their long backgrounds making things easier.
Gonna work out a build on this, in fact...I'll put the Strega in a blanked-up row at the bottom so you can see how it fits...
EDIT: OK, here we are. Thanks to Make Noise, we have this nifty "utility bar" in the middle of the case that'll come in handy.
UPPER: First thing there is a KonstantLabs PWRchekr, which lets you keep an eye on your DC rail health. Then instead of the XPOs, I opted for something even more over the top and put in a pair of Neutron Sound Dust of Time dual digital oscillators. Each one of those contains TWO oscillators for a total of four; in theory, you could actually use the build as a 4-voice paraphonic synth. The DoTs also have MIDI inputs, plus a pile of other surprises. And they can also receive updates as well as third-party oscillator models. Left the Moddemix by these in case you want to ring-mod the oscillators together. Then the first Codex Modulex quad VCA (a Veils clone) lets you maintain the stereo balance; just run the LEFT outputs to VCAs 1 and 2, then take output 2, and the RIGHT outs go to 3 and 4, with their output being on out 4. Feed outs 2 and 4 to the QPAS...but now, they're under VCA control.
QPAS, of course, is still in here...but with another Codex Modulex quad VCA after it. This is where things get even wackier, because you can now use TWO output pairs from the QPAS, with VCA control over both pairs. This set of VCAs can feed directly to the mixer in the lower row, but what I would suggest is to use that utility row and two of those mult busses to split the 2 and 4 outs from this VCA set and then feed them to the mixer AND the Beads in parallel. We'll see how those are dealt with in a sec. But anyway, the Beads (instead of just a stereo reverb) allows loads of granular screwing-around in addition to being a mere reverb. Now things get weird...
From the Beads, you can send its outputs on to the After Later VCA (or you can split its inputs off of that with mult busses 3 and 4) or it can go directly to the Doepfer mixer OR to the Happy Nerding 4x Stereo Mix. With that, you can run your mult busses as "aux"-like sends, and even split the last quad VCA out to feed the Beads and the VCAs simultaneously. Those VCAs, btw, give you level control over whatever is after them, and for the Rangoon's summing from stereo to its mono input. Or, or, or...suffice to say, I left that pretty open-ended so that you can adapt the mixbus and its send/returns however you like. And like I said, Rangoon is last, and it provides the physically-modeled resonator that's the Rings clone...with an extra trick or two.
LOWER: Your Tempi/Rene mkii stays where it is, and it's a great choice for both control AND sequencing. Then Ochd, Maths...and new stuff, in this case a Frap 321 and another After Later VCA pair. This is what I sometimes refer to (in its various forms) as your "modulation core"...it lets you modify your modulation signals in a pile of ways. After that, there's a Zadar + Nin for all of the envelope generation.
And then, the mixers. Plural. And this is so that, if desired, you can PARALLEL your effects processors via the 4x Stereo Mix by sending the Beads and the Rangoon's outputs to two stereo pairs, then take your synth feeds through the Doepfer mixer for panning and level adjustment. The Doepfer would then get sent on to the third or fourth 4x input pairs, and you can directly control the balance between FX and synth via that little thing. As for the Doepfer, it's got four mono ins with panning, so in theory you could go directly off of the second quad VCA's individual outs for both level control AND discrete mixing. Of course, I left lots of that rather open-ended so that you can easily vary the mixer/FX routing and balancing via a few different methods, not merely one fixed method. Last, the Strega is down below so you can get an idea of how it would fit into this; it's not actually in the build per se.
(TBH, as far as the Strega goes, I would strongly suggest getting the 0-Ctrl and 0-Coast to go with it, then cram them into THIS: https://reverb.com/item/39263230-3dwaves-triple-tier-stands-for-the-make-noise-0-coast-0-ctrl-strega-semi-modular-synthesizers That would give you a whole SECOND patchable system so that you can easily ping back and forth between it and this build...which would be just bonkers, really.)
So, yeah...at $5k+, it's certainly NOT what I would call "cheap"...but it IS capable of a hella lot of magic tricks.