date formula

Hi. I ran into a few problems while working with date formulas and couldn't find a solution anywhere.
I have a column with tenants lease expiration date. I entered a countdown formula in one column and the next column have another formula to inform when the lease is about to expire (90 days in advance).
What i was trying to figure out is how to tell the formula to show "expired" once the lease is past due and the countdown formula to show something other than the #NUM! error (could be negative numbers) when the date is in the past.
One more thing: Is there any way to avoid the #NUM! error message when cells are blank?
Example file attached.
Thanks.