Importing a worksheet into a new document

"If I "add a new sheet", I can copy and paste the content from another worksheet, but I have to create the same number of columns and rows in order for the worksheets to match."

That's because you are copying the content of the table, not the table itself. Numbers, text and formulas in cells are 'content'; fill colours and images in cells are format.

If you select the Table (Click a cell, to make the table active, and display its column and row reference tabs), then click the 'bullseye' at the intersection of the column and row reference tabs)to select the Table,

Then press command-C to copy the selection,

You get a copy of the table, including the content and format(s) of its cells.

Move to the destination document, choose the destination Sheet, and press command-V, and the Table, complete with contents and formatting, will be pasted onto the selected Sheet.

If you have other Objects on the source sheet, and want those to be included in the destination sheet, then:

After selecting the Table (an object), press command-A to Select All (objects).

Then copy, and proceed from there.

Regards,

Barry