Hey Aaron,
The reason for the first 2 fields you are unable to choose the other fields is because you can only choose Unique fields in the dropdown (i.e. RecordID).
But when you choose the field on screen you will be able to choose the fields, LeadTimeUOM & Name from the Wizard. On step 4 and 6 you can choose the drowndown choices and put in filters to have it restricted in what you wanted displayed.
TimeModifiedAccounting comes from QuickBooks TimeModified field. It is a predefined table field, tables that don't have a predefined LastModifiedDate field, will not keep timestamp information.
I hope that makes it clear, let me know if you need me to elaborate.
- Mortaza