How to create a data entry form that can submit multiple entries/rows of data in one go?

Well if you always wanted to enter data that way then have a table for the header information  and then a child table of the detail expenses.  Then you simply will do a lookup from that header info to the details for the common information.

So the issue is really how you are designing your app.

Here is some help on setting up relationships.

https://help.quickbase.com/user-assistance/about_relationships.html