Well, your second attempt to build a synth will work. But it's a very limited build.
I would suggest one of Intellijel's cases with the 1U row.
Your Cascade module is $100US and offers 3 attenuverters. An Intellijel 1U Quadrat will give you the same functionality with FOUR attenuverters for $80. You can use your Cascade to address 3 CV signals, three audio signals or a combination of both. You'll use them up quickly.
Peaks is a jack-of-all-trades module... but breaks down pretty quickly if you need more than one type of function. For instance if you want TWO envelopes you can only directly control the attack and decay. It's not bad... but it's very limited.
Basically, what you've built is a two oscillator synth that's pretty plain. You'd be better off buying a synth voice module (a module that contains everything you need to produce a basic synth sound). You could even start with a semi modular synth and then add a rack of stuff to it.
Spend some more time in VCV and up your budget. I'd really see if you can find a semi-modular that's compatible with Eurorack as your entry point into Eurorack. You'll have less heartache and start with a complete synth, MIDI interface, etc.