Hi there!
Thanks for your query.
You can lower the padding value to reduce the cell height. Here is a sample code you need to put on your custom CSS:
.sppb-addon-table-main td {
padding: 10px 20px;
}
Note: Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.
For your second question, would you please explain it more? I could not understand what do you mean by making groups, and how?
Unfortunately, there is no way to upload .xls within the table addon, you need to put elements by hand.
Best Regards