Here's what I see... I'm not trying to beat up on your decisions. But I see a lot of issues.
First, don't rack mount the Behringer. Your Eurorack space is expensive and the Boog is huge. Use that rack space for more modules. You can always patch to and from the Boog next to your rack.
There's a complete lack of LFOs. There's one in the Boog but it's extremely basic.
Envelopes. You have one envelope. But it's just a standard ADSR with no frills. Check out the Tip Top Audio Z4000NS. You get a ton more features including the ability to modulate each stage of the ADSR. That will be helpful for ambient in my opinion. You probably want more than one ADSR in your rig.
Filters? Filters can shape, blend your sound and modulate it when connected to modulators. There are many types and set-ups. I would investigate a two channel multi-mode filter.
Sequencers? Are you going to run this as a stand alone rack or connect it to your DAW? Both? How are you going to generate CV, gates, triggers?
VCAs? What's on the Boog isn't going to cut it.
Utilities? Buffered Mults, logic modules, envelope followers, quantizers, etc., there's an entire subset of utilities that you should have.
My thought is this. You're not ready to put together a rack. You need to learn more of the basics before spending your money so you're not wasting it or regretting your decisions. I would download VCV rack (it's free) and start patching. I think there's a virtual "Clouds" simulator in it as well other digital versions of Mutable modules. Put in the rack 2-4 ADSRs, a sequencer, two to three VCOs, and lots of VCAs. Make some things and modulate them.