2c. If it is not flushing away completely there is a blockage downstream which needs to be cleared.
3. If its the overflow, then:
3a. It should never really have water in it, and if it does, then the water softener needs attention.
3b. Points 2b and 2c also apply.
4. Yes, it needs attention. However, as it must have taken some time to get in that state, its hard to see that it is urgent.
5. Check and clear any blockage in the pipe downstream.