Freeride/Downhill advice needed

Obviously you can change any components on your bike but to answer your question the fork, shock, brakes, derailleurs (drivetrain) are the parts most often upgraded as new models come out. For brands, I will say and most people will agree that Fox make the best forks/shocks out there. If your into downhill/freeride, Fox 40's are the way to go. When it comes to the brakes, derailleurs, and cranks, personally I prefer Shimano Saint. Sram and Formula also make top of the line brakes. For what concerns the wheels, I recommend Maxxis for tires, Mavic for the wheel and Hope for hubs. Hope this helps

Alright, so. The NS Core is a hard tail, so a Fox 40 really isn't an option, and I'm a Rock Shox man myself. But that Marzocci looks like it has enough travel for a hard tail to survive. You're just gonna have to manhandle that thing. A bit higher oil level will firm it up. Shimano's great and so is Sram. Just wear out whatever drivetrain you have. If your're looking at serious down hill, good hydraulic brakes are highly recomended. Other than that, make the cockpit your own, meaning stem and bars and lever angle and shifter position. Wide bars are good for control and the stem reach is up to you and your frame. Ride On.

Generally, when we refer to "The drive train" that means the chainrings, chain and cassette. The real working parts that wear out the fastest. A derailleur and especially cranks and BB can last through many many drivetrains. The parts of a drivetrain will wear down slowly together, so they are typically all replaced at the same time. As I said before though, there's not a huge difference between the major makers in terms of performance. At least not enough to switch them out before they are worn out.