That's a lot of questions so I'll answer a few, and let others have at the rest.
For your use the Xterra is great out of the box. Slap some AT tires on it if you want, and you're ready to go.
The SC option is the only "new" part of the powerplant. The Xterra V6 has been around a long time, so no surprises there. The SC only gives you an extra 40 hp, and requires premium gas. The standard V6 hovers around 16-18 mpg average, so premium can get spendy.
The 2002 Xterra has the e-brake on the floor, which is an issue for the 5-spd drivers out there when offroading. Grab a 2001 if this is an issue for you. Otherwise go Auto.
Aftermarket options for the Xterra are just starting to appear. But like I said, some good tires, and (maybe) some Bilstein shocks for a smoother ride and you're ready to go.
Low maintainence, and a lot of fun, you would be joining a lot of satisfied customers who own this truck.