Some basic remarks although I'm not the most 'expert' here.
For 'experimental drone/ambient-like/random/generative stuff' you will need many modulations. In a small case, DivKid Ochd (8 Lfos in 4HP) is worth considering.
The A-180-2 can easily be replaced by passive multiples like Black Market Monomults or Tiptop Stackables: you will save some space. You can even replace it by a buffered mult which is very recommended for a better distribution of the v/oct signals.
Concerning the empty 4HP, a recommendation often shared: the Disting mk4, the famous Swiss knife of the Eurorack.
To conclude, but you will need a little more place, listen carefully to the NE Demodus Versio. This is a tool that may be suitable for your musical orientation. A flexible and modern module with the possibility to change the firmware.
PS: a larger case... sorry :))
'On ne devrait jamais quitter Montauban' (Fernand Naudin).