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.
The Bicycle Repair Shop is the place to be if you want to buy a new bike, need a repair or to rent a bike. These guy know everything about bikes and then some and at an amazing price. If you need your bike repaired they go above and beyond to help you get your bike repaired. If you are a tourist the shop has a great many bikes to choose from at an excellent price. I visited this shop last time I was in Seattle visiting my son and we rented the tandem bike it was a blast. My son bought a great bike and if he needs a tune up he goes to The Bicycle Repair Shop. This is the best bike shop in all of Seattle !!!!!!!
Whether you ride a single, 7, or 10 speed bike or anything in between, you will need a slightly different chain. The major difference is that they come in varying widths to accomodate the different spaces between the gears, but quality of construction is also a factor in choosing a chain. Inspecing the chain should be a part of your regular cycle maintenance procedure- It’s important to keep a chain well lubricated, but oil will also attract dirt and so different oils for specific riding conditions are available. Remember to clean your chain regularly to get the longest life out of it and the gears.