A wrench that fits the hub nuts:   If your bike has quick release front and rear wheels, you don’t need this, but if you have an internal hub on the back, such as the NuVinci, a wrench that fits is a great idea.  99% of the time, this is a 15mm wrench, but you should check your bike.   A 6 inch adjustable wrench can also work, but it will be heavier, and when using an adjustable wrench, you do need to take more care to not round over the nuts.   A fixed wrench is the best choice.    Some multi-tools have a 15 mm wrench built in, but again, if you have limited hand strength, something with more leverage is a great idea.
Main types of bicycles are road, mountain, commuter/comfort and fitness bikes. There are more specific types and other names for bike types within that, such as urban bikes (same as commuter bikes), cruiser bikes, dual-sport bikes, hybrid bikes, fixed-gear bikes, cyclo-cross bikes, adventure road bikes (aka  all-road bikes, gravel bikes), road bikes, touring bikes and specialty bikes, like BMX.
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.
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