I think this looks like a great start, and you don't need much more to get going.

One suggestion would be to find a way to generate CVs for notes and triggers. For example, with an FH-2 from Expert Sleepers, you can connect a USB midi keyboard to trigger and play different notes on the Plaits. Without a keyboard, there are a couple of other options. You could add a small sequencer (e.g., SEEK from Copper Traces). You could add a bigger sequencer (e.g., Rene2) but then you would also need a clock (e.g., Pamela's New Workout), and then you are well on your way down the rabbit hole. You could add a quantizer, and let the Maths drive the tones. Or, you could add a random generator (e.g., Marbles from Mutable Instruments) for triggers and notes.

Other than that, I can recommend a Disting Mk IV. It is the Swiss army knife of modules. It can be a quantizer, random generator, sample player, recorder, envelope generator, LFO, VCO, or fifty other things, all by itself. It is great for learning what module you need next. E.g, if you always end up using it as an LFO, then you need a dedicated LFO.