Next to everything else that might go wrong with a bicycle on an extended ride, a flat is a relatively minor issue that can be easily repaired trailside, if the right tools are at hand. If they aren’t, a quick fix can turn into a long walk. Well-prepared riders will perform a tune-up regularly and clean their bikes after every ride. For the less-diligent, a well-stocked repair kit will suffice.
The Bicycle Repair Shop does rentals by the hour or by the day. They have reasonable rates. They have solid, lightweight hybrid bikes so you can tackle train tracks and brick streets and hills. They also have road bikes for the more experienced. You can reserve online in advance. You get a helmet and a lock with your rental. The staff in the shop are friendly and will suggest routes and point out hills if you're new to the area. And believe me these hills are no joke!
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.