Hi Caesarises, I saw your post and felt some sympathy with your situation. The Prophet 12 is certainly an awesome beast and you are brave to have 'jumped in the deep end'.
I don't think I am well placed to offer tuition as I am self taught, and only interested in creating original and flexible voices. I started (in 1978) playing violin through a 1 oscillator and 2 filters mono synth. Later I fed an organ through the synth, but it was all simple filter modulation, a bit like using 1 oscillator and the filter knobs on the Prophet. I spent 30 years programming and playing a Yamaha DX7, but the FM (frequency modulation) set up on the Prophet 12 is different, and in some ways more sophisticated (the DX7 only used Sine waves).
I recommend spending some time exploring Timbre. Instead of just adding waves in parallel, explore what happens when you synch one waveform to another different one. For FM modulation just use Sine waves, or Tines, Mellow or Muted to start with, the more complex Waveforms impart too much of their own character which makes it harder to hear the FM effects.
It will be a steep learning curve for you, but you can make life easier by using a preset with the dynamics you require (Piano, Organ etc) and then just playing around changing the Waveforms and modulation. One issue to watch out for is Panning. If the pan is spread too wide every other note jumps between the left and right speaker (I have even more of a problem here because I am running in quadraphonic). Maybe if you avoid pan it will help with the volume drops.
I am sure other Forum members will be able to offer good advice, there are some very experienced and knowledgable people here. Good Luck, and try to have fun. It has taken me 3 years to write 250 voices, but now I am free to just play!