Hi Boann,
When I was in research, we always said it was the questions you asked yourself that made progress.
With PD however, we are all suffering different problems, and you might find the priorities vary. For my own case, My order of prioities would be
1. Motor symptoms 2.neuroprotection 3 non motor symptoms. However there is bound to be some who would give a different order. So much depends on whether the neurons are totally dead or just deactivated. Would research on neuroprotection be likely to produce results which would stop the rot, ie stop progression only, or turn the clock back and regenerate the neurons, or both.
As regards side effects, I can only think it must be better never to develop side effects in the first place, and aim for a non side effect treatment, ie your number 2.
While we are asking ourselves questions, there is talk of forcing the brain to rewire itself, and take alternative pathways, by for example walking with the apparatus which puts pictures of tiles in front of your eyes. See the thread Technology Helps Parkinson's Patients Walk Safely Again
I have for the past 10 days tried walking on the kitchen tiles and deciding which tile I am going to step on in advance. If this forces the brain to find alternate pathways, should I do this unmedicated or medicated. I can find arguments for both.
Ron