In my experience steps 3 and 4 above have to be done separately. In cases where I've added a lot of problems (e.g. twice as many as I need) my workflow usually looks like this:
1. An initial purge of surplus problems: select for deletion and save.
2. Reorder the remaining problems; save.
3. Delete any additional problems to get the number down to what was promised to the students; save.
4. Edit any individual problems as needed.