What is the name of your state? NJ
Tenant vacated the premises 4 days prior to the eviction proceeding. I sent a letter with the itemized disposition of the security deposit via certified mail and regular mail within the 30 days required. Tenant still has a balance that they owe plus they left before the lease expired. Should I submit my small claims before the unit is re-rented or after?

Re-rent the property first so that you KNOW your damages/costs for securing a new tenant.

You should consider your option for actually getting any money from tenants you have evicted v your time and energy...if you are talking $500 it may not be worth it - if you are talking $5,000 it may be worth it.

Thanks for the quick response. The balance is 2K without any late fees, etc... Monthly rent is $1,550. I gave them 20 days to pay the balance and made them aware of their liability for the rest of the lease. The tenant's parent also signed the lease and the parent owns property so I hopefully can get it one way or the other.

Your communication should be with the co-signor as well as your evicted tenants.
Once you know your total costs, write them a letter and give them 10 days to pay you by bank or certified funds and then sue them.