The best advice is to start slow. Get only a few modules at a time. Learn them and figure out what modules to get next as you figure out a workflow
Just spitballing modules that I'd want to include...
Sound Generation:
Quad Drum + Qex expander or Erica Synths LXR should be on the top of your list for drum sounds. Either of these alone could start banging out beats with a sequencer (like Beatstep).
Basimilus Iteritas Alter is THE king of kicks, but Kickain is a newer option that looks really good too
Check out Percall if your thinking about creating drum sounds from "scratch" with oscillators and noise
Sequencing:
Euclidian Circles
Varigate 8+ with Voltage Block is an incredible combo for sequencing gates and stepped modulation
Check out the full suite of 4ms clock modules (+ expanders). Rotating Clock Divider is an all-time favorite. Quad Clock Distributer and Shuffling Clock Multiplier+ are all amazing. Pingable Envelope Generator for modulation
There's a lot of rhythmic fun to be had with gate generators like Grids, Zularic/Numetic, Knights Gallop and Moffenzeef MITO. Add in some logic and sequential switches for more variety.
Pamela's Workout is useful in every rack
Mixers:
Jumble Henge
Tesseract mixers + output module or Cosmix
Effects:
Tons of great choices for multi effects or specialized reverbs/delays. FX Aid sounds great and has many algorithms.