Do I have to populate every Account Configuration even if it does not apply to my lease portfolio?

Yes. You will have to assign an account to each Account Configuration to populate journal entries for each lease. Note- the reason for this is that although an Account Configuration may not apply to your portfolio it might in the future. For example, you might not currently have/need a gain/loss on termination account but in the future you might terminate a lease.

Tip for success- some customers have found it useless to create an account called "Not Applicable" as a ledger account and map it to Account Configurations that do not apply to their portfolio.