I've had the System 10.1 for about a week and wanted to get a feel for it before I looked into other things, since it's my first modular. Now that I've been playing with it, I've got a long (very expensive) list of things I'd love to add, but this plan here is just my next steps, and things I can afford now or soon. (I'd LOVE to get an Intellijel Metropolis sooooo much, but I can't do any $500+ modules right now.) On its own, the System 10 is a real nice monosynth and you can do some neat stuff with it, but I want more than a monosynth. I want more things to play with... more sound sources... more triggers... more CV sources... more performance inputs...
My first goals are to get more VCOs and LFOs and VCAs. Also, I want some reverb.
The Qu Bit will have the reverb covered (until I can afford a bigger awesomer one).
The Lightstrip seems like an awesome, small, and inexpensive little quick CV/gate source, and with the looping function it can be an LFO in some cases. And as much as I love my little midi keyboard, it'd be nice not to need it all the time for my modular.
But the VERY FIRST addition I'm going to make is the Peaks. That's got LFO covered (2 of them!), but it can also be so many other things... It's got ADSR (2 of them!), it's got drums (bassdrum + snare drum!), and it's got a mini-sequencer! This is the most feature packed thing I've seen for this price.
This plan is still a work-in-progress. I'm also considering a MakeNoise Function in place of the Peaks, and I'd like a noise source and S&H, though that's not quite as important (at this stage) if I get the Peaks. I still have no idea what to do for more VCOs or VCAs yet. Plus I think most of what I buy is going to come from local shops (NYC, so there's a few) since I'm horribly impatient when it comes to this and don't want to wait for mail to arrive, so it depends on what they have in stock and recommend.