Hi! Welcome!
You've got a basic entry level rigid bike. It has a 1-1/8" headset and is equipped with V-brakes.
Suspension wise, it should work well with any decent suspension fork with relatively short travel.... I'd aim for 80mm. The fork will need to be equipped with a 1-1/8" steerer tube of sufficient length for your frame, headset and stem's stack height. Options abound. I recently fitted my wife's rather similar bike (Spec. Hardrock AX) with a Magura Asgard 100 fork - Goes very well, despite the added height. The Pace RC36 would seem a good choice (uncommon over here, I've never seen them in the wild!).
Brake wise, you're probably fairly limited. Unless the frame is equipped with disk caliper mount, and you wish to change your wheels, you're pretty much gonna stick with V-brakes. They are easy to install, set up and maintain. In all likelihood, yours could still serve well, with just new cables and pads. There isn't much performance difference between entry level and top end Vbrakes, beyond weight savings and styling.
If you wished, after installing a suspension fork, you could upgrade to a disk in front, at the expense of a new wheel to carry the rotor. I did this on my wife's bike, and it worked well with Avid BB-5 disk - giving similar performance to the V-brakes in dry and much better in wet.
Transmission wise, you can pretty much use what you like. It all performs similarly, though higher quality bits will work more smoothely and last longer than cheap stuff, it's all serviceable and largely interchangeable. I'd suggest SLX or higher grade kit. If you change the cassette to one with a greater number of gears, you'll need to change the shifter to match.
It's all up to you! Bikes are pretty modular (or were, until modern times began messing with standards left and right!), so upgrading is pretty free.
J
