Take a look at my Add-Ins:
Feel free to modify these to suit your needs.
The first one launches a UserForm (custom dialog) that lets the user choose what goes in the stamp (or type what they want).

There are a total of nine in the list and, again, the user can type unique content because it is a Combobox.
Here is a sample of four of the stamps.

The second one has only a PAID stamp.

Both use the same techniques for inserting the stamps. They are WordArt and stored in AutoText.
These do not use fields for the date, which are not static, but rather use vba to insert the date as text. The one with the drop-down is a bit more sophisticated. With the second one, it is difficult for anyone to change the date. The second one uses the user name to add the name.
The same techniques could be used by you to create multi-line stamps.