So yesterday I bought myself a trek 520 from some guy who just had it rotting in his garage. I bought the bike for 100 bucks, and it's a great bike, but I wanted to change some stuff out. Right now, I have all of the Shimano 600 groupset on the bike except for the crankset and the cassette. The crankset on there has 3 gears, and the bike just skips the middle gear. The cassette has 5 gears on it. Also, I would like to be able to put Shimano STI shifting on there rather than the current downtube shifting for a reasonable price.
Does anybody have any suggestions for what I should replace my crankset and my cassette with to make my life easier for adding STI shifting? I'm quite a newby, so I don't really know if the current derailleurs will shift with an STI set up. Anyways, I'll take whatever advice I can get. I really want this bike to be a learning experience and use it to intimately understand bicycles. Thanks!