definitely can recommend ExplodingShed, their support and shipment are super fast. Also great super friendly guys working in the shop. I just wished they had a larger catalogue but for their size it's understandable that the risk of overstocking and having a large catalogue is too high. Regarding Brexit it's unfortunately a reality now and I don't think we can "undo" it, but I think there could be a few options specifically for Thonk. I think it would be great if they opened a store in mainland Europe to provide for their customers outside of UK. This would mean a split in terms of management and a lot of coordination but anything can be achieved with the right motivation and proper planning. Maybe my view is too simplistic and I'm not taking a lot of "buts" into account.

I'd recommend to use Arduino as a platform to practice and understand the basics but at some point the processing power and limitations of an 8-bit processor will make you hit a roadblock depending on what your goals are. On the other hand the ARM-environment is great and cheap, check out the blue pill/black pill boards. No wonder why so many digital modules have M3s and M4s inside. (Varigate, QuadLFO have ARM processors, Mutable Instuments uses them in a lot of modules, list is endless...). You can get ARM boards for 1-3$ from China (check out AliExpress).

Cinnamon is a definite recommendation, small footprint for a SVF with built-in distortion and input-related cutoff frequency modulation. I couldn't get my hands on the DIY kit since they were out of stock for months so I invested some of the lock-down time to build my own replica based on their schematics. In addition to that it uses the same IC as the Xone Filters in the A&H Xone 42/92 series. Maybe I'm biased because of that ^^ It's a quite straightforward design if you have some experience with filters.