Thanks all for the quick replies.
Indeed, there is a lack of VCA and utilities and I feel a bit tight in this case for the futur (wasn't expected to dive so fast into modular), so Mantis would be a great option. I will look for a used rack.
For Maths, I didn't think it was a priority due to the Batumi/Zadar/Samara trio. Will it make a huge difference to combine all of these ?
Here is the way I think it could be great to go (still think a multimode filter could be a good addition but don't know if the Happy Nerding 3 VCA will be enough or if I preferably go to something like the Intellijel Quad VCA) :