Have you looked into filters or VCAs? Unless you plan on running everything through the benjolin all the time, an extra filter with a big ol knoby knob would be great for sweeping the Black Wavetable. A VCA can help get get some really weird sounds going. Modulating your modulators and all that. If you downsized your clouds clone you should be able to squeeze both in comfortably.
For the midi/cv you could save rack space and get a keystep or some type of external midi/cv converter.
Those Caixa cases look great, lots of functionality, which would probably cover your € per Hp between the cases you mentioned. Caixa is €6.37 per hp, the rack brute is €2.15, and the mantis is €1.53. There's always trade offs, In this scenario it's rack space vs physical space vs built in functionality vs cost. Personally, I'd go for a mantis, put in the utility modules I need (and also choose, which is important to me) and then have room to add whatever later on when I start figuring out what's missing
Just some thoughts, have fun!