The fabric attachment system is low-tech, but that seems to be helpful, as it can adapt to seat rails of different widths. One fancier option you might see on more expensive seat bags is a quick-release mount that you install under your saddle. But those have a fixed width, and therefore can fit under seats with only those exact specs. Brooks saddles, for example, are too wide for these mounts.
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.
On a very sunny Saturday I had a rear spoke break - you can imagine that no shop was willing to promise a quick repair! I was so fortunate to find this shop and will come back - Andy not only told me to come down and he'd get it fixed, he had his assistant work with another couple while he measured, cut to the right size, installed and trued the wheel while I waited! It was awesome, and the whole place had a great feel and good people. Best of all he charged a very fair $20 for all that work - I would have paid a premium for the quick service! After experiencing lots of attitude at other shops and poor service, this was a real find. I hope you will check them out, they have a great selection of bikes and accessories too! Good people and good craftsmanship should be rewarded.
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.