I rode my bike across the country last summer so I badly need to replace my cogs / cassette. I have a Giant Defy 1 with

cranks FSA Gossamer MegaExo, 30/39/50
cassette Shimano 105 12/27, 10-speed

Are there any other parts I might want to replace (aside from the chain)? Do the teeth on the derailleur wear out at about the same time? Probably a stupid question, but I'm new to actually doing any work on my bike, lol