Freddy pretty much cut to the chase on this. Good advice.
(1) Once you open a tin, depending on the blend, as well as the ambient temperature and humidity in your storage location, it stays reasonably fresh for 3-4 weeks on average. If you've got a lot of tins and/or baggies open, and/or you don't think you'll be smoking the contents of the tin/bagge in a month or so, jar it. You can also find that using a humidification device, such as an aluminum disk/coin or HumiCare pack, useful -- you can find these in smoke shops for $1 or less.
(2) Aromatics as a rule do not fare well during long term storage. They don't "go bad," but because they are topped with flavorings, those flavors will flatten out with time and eventually mellow out to oblivion. That said, many virginia based aromatics are still pretty damn tasty, since the virginias sweeten and improve overall. Aromatics, properly sealed, IMO, keep well for about a year with little discernible degradation.
(3) Sure, tins can rust. I've received tins from vendors with both external rust and some with internal rust, although this was quite rare. Sealed undamaged tins, stored in a cool, dry, dark cellar should not pose a problem.
(4) Yes. If you use new jars, they do not have to be washed. If you reuse a jar and it has been used for anything other than tobacco, wash it (including the lid) with dish soap and hot water, or on hot cycle in a dishwasher (I would replace the lid if the jar was used for food, lids are cheap and I don't like pickle flavored tobacco). You can reuse a jar and lid that was used for tobacco -- certain blends, i.e., aromatics, lakelands, certain English blends, can ghost the jar, so keep the same types in the same jars, or simply wash the jar and the lid before refilling it. It's also important to rinse and dry the jar and lid thoroughly after washing.