Hi Ronbo!
I've used my modular for drum processing a ton. While you don't NEED an envelope follower, they're really, really useful. The other thing that's useful in that situation is buffered mults. The ones in your rack are unbuffered, which could cause signal level drops. Depending on how you're getting signal from outside your modular into your modular, you might need an input module too (the Doepfer A-119 is both an envelope follower and an external input). The other comment I have is that you have two oscs and three LPFs. Unless you're just in love with the LPF sound, I'd encourage you to consider at least one multimode filter (like Intellijel's Polaris). Often times they have one out per mode, so you get more audio to do fun things with.
Have fun!