I agree with all of the above replies and will add my 2 cents:
Start off small, experiment and learn. I think the initial setup you have there is a really good start and will be able to make some interesting sounds right away. Maths is an amazing module and the STO will sounds great and give you a sub octave out that can be used to get sort of second voicing. One thing you might to consider is instead of the Optomix, take a look at the Make Noise Dynamix. Works great as a mixer, VCA and can do side-chaining fx as well. Since you have a Digitakt, a midi to CV module like the Mutant Brain will allow you to get tight sequencing and melodies out this setup right away so spring for that if you can.