Man, if you're starting out and you know you'll need several components for a bag... just get this. It will save you so much time picking everything out that even if you balk at the price (amazing value, by the way) I bet that if you did the math using your hourly wage and the time spent picking everything out and making sure it fits... you'd save a lot of money and a lot of irritation if you just got this. Just get this.
Patch kit: Patch kits are easy to use, light and compact, and if you get more than one flat on a ride (it happens more than you’d expect), it can save you when you’ve already used your spare tube. Plus, on a rear wheel, patching a tube can be faster than replacing it, as you can often do this without removing the wheel at all. Another upcoming post is going to show you how to patch a tube.
Modern bottom brackets use a sealed bearing type construction that keeps water and debris locked out, so they seldom go wrong. Maintenance is impossible so they need replacing when they do wear out. Older style cup bottom brackets need to be re-greased every now and again, and occasionally will need to have their bearings replaced. There are a lot more teeth on the chainring cogs than those on the rear cassette, so need changing less regularly. Cranks usually a solid one piece construction so there is not much to go wrong.