ServiceNow Bulk API Insert Importset Records

Hello All,

My questions pertains to how the ServiceNow Bulk API activity Insert Importset Records works.
Specifically, how it maps fields to the ServiceNow staging table. The ServiceNow Object Activity Insert ServiceNow ImportSet has a wizard to manually add or delete fields but the Bulk API activity doesn’t appear to have this functionality.

I am also curious regarding the number of records that can be sent at a time. I have 40000 records to process in a spreadsheet. Is there a limitation? Which activity would be best suited for this task?

Lastly, the responseStatus output variable only has 3 fields, success, error code and message. There is no property called statusmessage, which I see in a POSTMAN JSON response. How would I get that additional value from the responseStatus output variable that is passed back?

Thanks in advance.