Can you send emails back to back to the some of the same contacts?

Can you send emails back to back to the some of the same contacts?

We'd like to send one email to 3000 people, and then the next day send a different email to ~1000 of those same people. Can we do this in zoho?
Can we upload both lists of ~4000 into zoho?
Do we need to delete the first list before importing the second? Will this make us lose some insights?