Hello alsonjonsolutions.

Thank You for Your purchase.

You'd need to enable the Scrollable slider under table's Display settings.

After that, add this code to the Custom JS and CSS under main Settings of wpDataTables:

.wpDataTablesWrapper div.wdtscroll {
    height: 310px;
}

You can edit it any way You'd like, of course. The result is shown in the attachment - 10 rows visible, others are scrollable. The only difference is that I don't have 100 rows in the table I created for testing purposes, but only about 20. Works good, that's the important thing.

As for removing the column header placeholder, You'd need to open the next file:

wp-content/plugins/wpdatatables/assets/js/wpdatatables/wdt.columnFilter.js

And simply delete the name of the placeholder for each of Your columns.

Example:

<input type="text" class="form-control wdt-filter-control text_filter" placeholder="Product">

Has the following result:

While this:

<input type="text" class="form-control wdt-filter-control text_filter" placeholder="">

Has the following result:

Please let me know if this helps.

Best regards.