I'm not terribly experienced giving feedback like this, so take this with a grain of salt, but here are my thoughts:
Bigger case. You're just gonna find yourself limited with 84 hp, no matter how you look at it. Particularly since you can only have 10 modules plugged into this case, regardless of how much hp you can squeeze out of it. The Nifty case has things going for it, no doubt (like the DAW connectivity), but you're just going to get frustrated saying "no" to interesting modules with a case this size when for only a module's amount more you can get something bigger (e.g., Mantis, etc..) that will allow you more flexibility.
The Grandmother already comes with a sequencer and arpeggiator, a filter that you can send a signal into, and a few other tricks. Use those and don'y waste space with modules like the 2HP Arp (it's a good module, but not a great use of space). Also, between Plait's natural abilities and the VCF on the Grandmother, the MI Ripples starts to seem unnecessary.
Triggers and LFOs. As you can see, I've done a lot to your rack. Moved your Pams to the left (personal preference) and gave it the expander. Pam's can do a lot of neat tricks (triggers, gates, logic, quantization, stepped/smooth random, limited envelopes, euclidean rhythms, etc.). You don't want to waste its regular outputs on something dull like a steady 1x trigger. Use the expander for that. Next, we have modulation. Your A-147-2 is awesome, but pretty big for that case. So, I went bigger. For 5 hp more, you get Batumi and it's expander, giving you up to 12 LFO outs. Plus it can be cv controlled, self-patched, and has a few neat rhythmic modes that will keep you busy.
Utilities and cv-futzers. More, you need more. Audio manglers sound nice, but the richness and movement and finesse in modular come from the ability to move, attenuate, switch, offset/invert, route, and otherwise f-up a signal, which is what utilities give. First, you have the Happy Nerding 3x MIA. Everybody needs attenuverters, and this is 1 more than the one you had already. Also, the double pots are great to play with. Then the A-130-2, dual VCAs, since you really can't have too many. I like to have VCAs after my LFOs so I can modulate the modulator. Then, the A-182-1, Switched Multiple. This module takes no power and allows you to manually send or mute signals to two different sources. It also acts as a 2 channel multiple. As simple as it is, I've found it essential to my patches. Then uO_C, which gives you access to a whole host of programs to try out, such as quantizers, sequencers, slew, clock dividers, envelopes, simple comparators, vcas, and logic, etc... I prefer it with Hemisphere loaded, but it's amazing either way. A bit menu-divey, but it will give you a sense of what utilities and tools you'll want to dedicate a standalone module to in the future. Then the endorphins.es Airstreamer for ADSR duties (and other things like slew, s/h, etc.). Unfortunately, envelopes were an area I couldn't really help with (aside from uO_C and Airstreamer), as I don't know of good dual (or more) envelope generators that are thin. If you had a few hp more you could go with some interesting options, but you are limited at the moment to 4 hp (see below about Plaits). At the end, I give you another Happy Nerding Module, the 3x VCA, since, you really can't have too many of them, and they work great as an end of chain module. Also, those double pots.
Audio. Plaits has got a big footprint, but I always prefer the real MI modules to clones. That said, with MI gone now, a clone like Knits would not be a bad or problematic choice. With Plait's/Knit's onboard abilities, you can do without an additional VCF, hence the removal of Ripples (no offense to a cool module intended). Then Beads. Beads is awesome. Beads stays. Be aware though, it takes some playing around with to get the sounds you want out of it. Once you figure it out though (and if you have enough modulation), it can really do wonders. With 3 hp left, I give you Erica Synths DSP, just a few more effects to play around with.
And there you have it. Should let you have a good time with your Grandmother and keep you flexible enough to experiment.
In the final assessment though, I think you have space to have fun, but you'd have a whole lot more fun with a bigger case.
Best of luck!