I'm not ready to make sounds or music yet, but I've done a whole lot of reading, and have purchased a bunch of parts that I did not already have on hand in my home electronics lab (mostly potentiometers, knobs, 1/8-inch mono plugs and jacks, op-amps, and the like), as well as some Vector rails (to complement the Synthrotek rails that I bought earlier).
I'm building an enclosure out of aluminum sheet and plate (I may be making a mistake, since it's going to be pretty heavy - I am building in some handles on the sides to help me move it around - it is using two 8U-height rack rails, which will give me 2 sections of 3U and 2 sections of 1U (PulpLogic 1U). I've also built a power supply and a power distribution rail.
I'm going to start by cloning some of the designs at
https://aisynthesis.com/, starting with a VCO, a mixer, and a VCF. I will also work on building a sequencer and some A-to-D sampling and some D-to-A outputs (possibly based on a Teensy microcontroller, including its well-regarded audio programming SDK) and will go from there.
I have also installed VCVRack on my Macbook, so that I can experiment with sounds and patches before I have any of my hardware working. So still a ways to go, but I'm finding it all very interesting...