For your first question, it sounds like one of the screens you are on is "Personal Property - Information" in the casualty interview. It asks for Description of Property, Date Acquired , Cost Basis, and Insurance reimbursement. If you want to lump all your home content into one figure, you can only use one "Date Acquired". You will have to come up with a date, probably an average age of the property. The date you use won't make a difference in your deduction, but I would use a date a least a year prior to the flood unless you recently purchased the home and contents.
For your next question, your loss will be calculated by what you enter on the next screen, "FMV before loss and FMV after loss" minus the insurance reimbursement you put on the previous screen, minus a $500 limitation. So you will have to do some math and make some estimates. If you know what your loss should be, and can estimate the FMV Before or After, you can figure what the other FMV has to be. The IRS allows you to use the repair cost as the loss, so the difference in the FMVs is the repair costs. In other words, the repair costs restored your property to the FMV before the flood. Here is one way to do it:
Calculate your loss before insurance reimbursement using the $117/sq ft rule. Then, estimate the FMV Before Loss. (You can use the internet to look for market values of your property and contents. This is difficult to do, but make a "good faith" estimate and keep your documentation. The IRS mentions that they understand this is difficult, in their article, FAQs for Disaster Victims - Casualty
Loss (Valuations and Sections 165 (i)).
Subtract the loss you calculated using the $117/sq ft from your estimate of the FMV Before Loss. This will give you the amount for the FMV After Loss. Now you have the 2 numbers you need for the Fair Market Value screen. When you get done, go back to the Deductions & Credit screen and scroll down to the Casualty Loss section. It should show your loss that you figured minus insurance reimbursement and the $500 limitation.
If it is easier to estimate the FMV After the loss you can figure it that way instead.
