It is not obvious how to insert multiple rows in a Google Docs spreadsheet anywhere in the spreadsheet. Google has a button to add a variable number of rows at the bottom of the sheet shown below, but no obvious button to insert anywhere in the sheet.
The key is to highlight the total number of rows you need to insert before inserting. You need to highlight existing rows (which may have data already in them) and right click in the area where the row numbers appear for the highlighted rows. For example, when you right click on 4 highlighted rows, you will get an option to “Insert 4 above” as shown in the below screenshot