Re: Is this what is was meant for?
Re: Is there a better way to show multiple tables within a DB?
Well, that is for you to decide.
Re: Can I control/set as default the shape properties of the DB rectangle?
Yes, you can with the following approach:
Before importing data from Excel, create a group node. (Either by dragging the group node template from the "Group Nodes" palette section into the editor or by using the CTRL+ALT+G shortcut.)
Adjust the visual features of the newly created group node to suit your needs.
Create a user-defined palette section (see "Edit" -> "Manage Palette").
Right-click the group node to open its context menu and choose "Add to Palette".
Double-click the group node template in your user-defined palette section to set it as default group node style.
Import data from Excel.
Re: How can I label the rectangle from the excel Col.A?
After choosing the desired data ranges in the Excel import settings, switch to tab "Presentation". In section "Nodes" there is an option "Label Text". Set its value to the property you want to use as label. Note, this option governs the label text for both group and normal nodes.