No, you do not need to DELETE the export or sync resource related to the first batch before starting the second.
The flow would be:
- Create import #1
- Create sync #1 referencing import #1
- Start executing sync #1
- When finished, check status on sync #1
- Create import #2
- Create sync #2 referencing import #2
- Start executing sync #2
- When finished, check status on sync #2
And so on.