One way to look at this is that there is only one "overview crop plan" at a time, but the farmer modifies it until satisfied. Thus, the first few versions are just proposals, but at some point the farmer has had enough, orders the seed, files for insurance, etc. At that point he's committed and so the last "overview crop plan" stands.
This is totally hypothetical, but given the problem statement as it stands it a reasonable assumption to keep moving.
Yes they are. Sorry for this typo.
That's right. Just paper to the ta of your section.
Hand in english text for each use case.
Hand in UML diagrams for use cases and entity classes.