Function Junction... not sure easier Maths... more like POOR MAN's Maths... but also just less of a module. I own one, but like many modules in modular... they provide some similar functionality, but ultimately are just different. Might look at Doepfer Dual ADSR or Instruo's Ceis (newly released V2) if you want an "easier" envelope generator.
Too many voices for the size of case is going to be a popular opinion/criticism. BUT... depending on the patch, swapping them out can make sense, so its not like you can't own them. Maybe just keep HP reserved for a combination of one staple and one swap. Going to be your call financially on that one...
Never tried Ghosts, and probably never will... Modular effects are great to have if you aren't going to be using a computer or outboard gear; but I prefer (outside of granular, simple delay/reverbs) to use in the box/outboard gear fx. The Arturia bundle is pretty sweet, but I understand not wanting more screen-time added to your day.
Also, look into DFAM.Being semi-modular, it can stand next to your rack and create so, so much. Is it perfect? No. Does it have annoying limitations? Yes. Do I still love it? Yes. Using varios midi devices really unlocks it.
Enjoy your journey!