Getting a suppressor doesn’t require a “permit”. Buying a used suppressor is the same process as buying a new one. Fill out a for 4 and wait. If he’s giving you a decent price break, I wouldn’t hesitate to buy a used one.
Never messed with it. If I was going to try anything subsonic it would be a .300 blackout or a .308. Are you thinking of just playing around with it or did you have a specific use in mind? Do you have a suppressor?
I wouldn’t wait for the snow. I’d plan on hunting that unit in mid to late September before the snow gets too bad. Dedicate as much time as you can to it and don’t shoot the first goat you see unless you’ve spent a lot of time scouting. Milk it for all it’s worth, you may never get this...