Please to bottom part use 140 pc fan with 3 pin or if you need controll then 4 pin for example Noctua NF-P14s
Please use glue (superglue) to connect part 2 with part 3 (middle part 1 with middle part 2) to connect it better you could use pin and first glue them to part 3 and then part 3 to part 2.
Fill part 3 with active carbon. It could be activated carbon aquarium with minimal diameter 3mm
Put part 4 on part 3 and use hepa filter (vacuum cleaner filter or its substitute for philips FC8031 or Electrolux AET 7740)