On the studded snow tires- I don't know right offhand why they wouldn't work. The bike comes with 26x2.125" tires. With those tires, there is very little clearance on the sides of the tires, but a reasonable amount of clearance outside. So if the tire was a tad taller, it should work, but no wider.
On the springer fork, I don't know. When I was a kid, we had an old Schwinn bicycle with a front fork like that. I don't recall it really being a big improvement in the ride, guess it helps some. I didn't figure it was worth the extra money and weight.