Ah, ok. thanks very much! So if I understand correctly, I could pick up a new cassette and it doesn't matter if it is a 12-25t or 12-26t or 11-34t (or anything else, although I know this will affect the gearing) and then adjust the new chain to properly fit the new cassette.

As for the crankset, it looks like some of the teeth are chipped. Maybe I just need to replace the chainrings on it?