Swapping the fork, you need one that is the same length, this is measured from the crown to the axle, this will possibly be called a suspension corrected fork. You need someone to sit on the bike while measuring though, because suspension forks are typically shorter when loaded, while solid forks are not. You also need to make sure that the new fork is the same type, threaded vs threadless. Looking at the Trek website it looks threaded, but I can't be 100% sure.

V brakes are usually very good, you need to have them adjusted properly though, and then learn how to adjust them for pad wear, using the barrel adjuster. Brakes should be adjusted with new pads, so that there is about 3mm (about 1/8th inch) between the pad and the rim with the brakes off, the barrel adjuster should be turned all the way in. As the brake pads wear you turn the barrel adjuster once in a while to bring it back to the 3mm. There are slots cut into the pads, when you can't see the slots anymore, you need new pads.

Some riders like me prefer using cartridge pads, the metal housing is permanently adjusted to brake properly, when the pads are worn, you pull out a pin and slide out the rubber part, then slide in a new one, restoring the barrel adjuster to it's original position.







There are only 2 times that disc brakes are really better then V brakes:

1) Under extreme loads, where there is extended braking, for example a steep downhill on a tandem. The problem is that rim brakes heat the rim, but the heat is quickly dissipated, under normal conditions. Under heavy loads with extended braking the heat can build faster then it can dissipate melting the tire or tube where it contacts the rim, this is not good for the rider or riders

2) Under very wet or muddy conditions, wet brakes of any type are less efficient (the hubs see less water then the rims do), and mud can grind a set of new pads to nothing in a single ride.