An easy change would be to change the FETs. Some or all of them. Suggestions would be 2N5457 or or MPF102. MPF102 would be lower gain than the 2N5457 which is lower than the J201. If you wanted to go all out you could measure the FETs and change the source resistors. For more info, you...
Exactly. Cornish is overrated. I like the SS3 and the OC-1. But, I've found lots of compressors and distortion boxes that I like more. Gilmour has used the HM-2 and still gets his signature sound. That tells me that he doesn't need Cornish for his sound. Actually, I really like the ST-2...
Not a fan of the Vertex hype but for me the Phoenix is a Zen with the voice knob hard-wired to the sweet spot. I always like getting rid of a knob, if I can. But, agreed, you can't go wrong with a Zen drive.
I have 5 suggestions: the Chauffeur, the Southern Belle, The Phoenix ultra (a three knob zen), the Dude and the madbean Laureate. All top notch low to medium gain overdrives. The Southern Belle and the Phoenix are super easy builds.
Juan is one of the authoritative sources for Big Muffs. The ultrastoner mids are nice. So are the hoof mids. I think I like the ultrastoner ones better.
I agree with maxl0rd that this isn't the best platform to learn how to code. It's hard enough when you know C++ and have embedded experience. I saw that from lots of experience.