I'm 5'8" and 275 lbs with a male body, and I'm still relatively new to bicycling. I didn't learn how to ride a bike until right before I turned 21, and I've only been riding regularly for about 11 months (I'm 23). I've never done maintenance or bought new parts, and I think both are just about in order right now. I currently have a 1987 Hard Rock Specialized hardtail mountain bike, and it works for me. The frame fits my proportions just right (it used to be my uncle's, and we have about the same proportions), it's good and sturdy, the handlebars are a good configuration for me, and it handles beautifully. I mostly use it for commuting on urban roads (I live in Silicon Valley). I'm looking to replace the pedals and tires, get a rear rack, maybe replace the wheels, and install a water bottle holder. Can anyone give me recommendations as to what specifics I should be looking at with these parts?