Hello Anirudh,
There is no limit for the fields creation how ever you can stop the creation of dynamic fields using one system property -- >Please follow below description
glide.import_set_row.dynamically_add_fields
Specifies whether an import set can add new columns to the staging table (true) or not (false). Instances that contain large numbers of import sets can sometimes become unresponsive when an import adds a column because the instance must alter every row in the staging table. In some cases, the database alter table action causes an outage. Setting this property to false prevents an import set from adding columns to the staging table and produces a log message. As a workaround, administrators can manually add a column to the staging table by creating a new dictionary entry and then reimporting the import set.
And for the second question yes it takes the calculated value from the row and column and it will be mapped to the staging table
For more info check for import set properties documentation in below link
https://docs.servicenow.com/en-US/bundle/sandiego-platform-administration/page/administer/import-sets/reference/r_ImportSetsProperties.html
Please accept the solution if it helps you and close the thread it might help other users with same query
thanks
