I think 2 years as a default would probably be alright, as long as there is a possibility to extend it. Going into more advanced future options, if you’re putting in an entry for a mortgage you could need up to 25 years of entry (1300 database entries!) where as if I’m just putting in a 1 year lease agreement for my apartment, a shorter term is fine.
It’s not quite possible to really plan for the future like this, because there is always changes in budgets – be it a raise or job change, getting a new car or whatever luxury item.
I do understand that your system doesn’t work quite the same way, I kind of went “Duh!” and realized how different, programmatically, your website is when compared to Google Calendar.
Thanks for the information and details.