If you don't care about getting muddy/wet if it rains, then you can skip the fenders for sure. As far as swapping the tires, you might be better off to buy a second set of wheels & just swap them on & off as you need them. The guy across the street from me does this with his cross bike. Slicks for riding the streets & more aggressive tread for the trails. Swapping wheelsets is a lot easier than swapping tires/tubes.