The chances of being questioned by the IRS are low. You'll get a letter from them asking for documentation of the deduction.
Yes, make a list of what all you think you contributed and write the estimated value out beside them to document what you donated.
No, you don't need purchase receipts. You are allowed to deduct the fair market value (FMV) OR original cost, which ever is less. That's the only reason you're asked about original cost. For the type of stuff you donated, it's always FMV. For inherited property, you "original cost" is FMV.
The $500 at a time rule is meaningless. It isn't going to put off the IRS, which goes by total
