Yes to everything that you said.

But because it was converted to business use, you need to run the gain/loss numbers two ways.

1. Run the calculations you said using the purchase price and total miles since purchase.  If the result is a gain, use this result.  If it is loss, go to #2.
2. Run the calculation you said using the Fair Market Value when it was converted, and total miles since it was converted.  If the result is a loss, use this result.  If it is a gain, go to #3.
3. There is neither a gain or loss.  Just enter the disposition date, and leave the sales price BLANK.

However, with less than 5% business usage, any gain or loss will likely be very minimal.  You may consider just going directly to #3.  🙂