I'm of the opinion that if you're gonna do something, you should do it right. Not saying you need to blow a couple grand for a more experienced riders bike, but if I were you (which I am actually in the process of buying my first bike!), I'd save up enough to get an entry level bike with one of the several reputable names in mountain biking. Specialized, Trek, Giant, etc all have good entry level options.
I also feel that once something starts breaking, especially with used equipment, a lot of the other components have likely had quite a bit of wear as well. That will start adding up quick, if they get to the point where they actually break. If you're mechanically inclined, you could probably prevent / fix a lot of that, but I think you'd do better putting that time and money into a new ride.