Hi Quantum,
Marbles and Morphagene are two completely different modules. I don't really see much overlap there.
Instead of the Contour, have you considered a Zadar? The contour seems like a two stage envelope generator with just attack and decay with some looping.
The Batumi needs a Poti. Look it up and you'll probably want it if you get the Batumi.
As for filters... I like the Morgasmatron due to its versatility. I have one. As far as a general filter module... this...
If you're wanting to sample external signals into the Morphagene then I'd upgrade the Intellijel Outs to the unit with inputs as well.
Deeper question: how do you intend to control your rack? This is where a sequencer or MIDI to CV comes in.
The Maths has two channels dedicated to attenuverting (channels 2 and 3). If you need to control the levels of some CV, then you can do it with this... though a dedicated attenuverter set would be more practical.