All the options related to the frontend submission system can be found in Theme Options -> Vehicles Submission
Listing Duration & Expire
If you wish to expire listings after a certain period you can do so by entering the number of days into the "Listing Duration" field. Simply enter the number of days and all listings submitted will expire after that specified amount of days.
Create a new page and select the "Submit Vehicle" page template. Once you're done, change the option "Submit Page" to reflect those changes.
Set Fields As Required
If you wish to set certain fields as required, you can do so by going into the "Fields Requirements" tab and check the fields that you wish to set as required.
If you wish to enable/disable certain emails, you can do so by navigating to the "Email Notifications" tab.