This is a state crime, not federal, so he can't pardon himself as president. I think he could if he was governor of New York, which seems like a long shot.
And New York's AG has seemed pretty keen on seizing his property if he wouldn't pay before. Idk if they can do that for these types of fines but I'm sure they will if they can.
How a small but violent subset of the nation would react. A significant number of people would be just fine with him going to jail and forget about him.
I can't imagine the RNC trying to scramble to get another candidate this close to the election. More likely as not he either pays a small fine. I doubt he'll get jailtimr. Knowing this country and how weird things have gotten he'll go to jail and his supporters will come out in droves to the ballot box and then win the presidency and we'll be in a really tough spot.
Which, if he's making appeals based off the verdict (thus profiting off a crime), those funds could be seized as well, I believe. (your mileage may vary, check with local jurisdictions for details)
Political campaign donations cannot pay for the Trump Organization’s lawsuit fines and I don’t think they can pay for his personal criminal legal fees.