There are multiple ways to change the line spacing.
Place the cursor in a paragraph and choose: Format > Paragraph… this invokes the Paragraph Formatting dialog. Change the Line Height field to 1 or 100%. Note that the extra white space after the paragraph is not related the Line Height. This can be removed by setting the Margin fields in the Spacing tab of the same dialog to 0.
Repeat the above scenario for each paragraph. Note this can be time consuming process, therefore I would advise to create a stylesheet rule for the p element (assuming that you want to change line height for all paragraphs). Stylesheets are applied to all elements that match the selector of the stylesheet.
To create a new stylesheet rule choose: Edit > Stylesheets… The Stylesheets dialog is shown. Click New, the New Rule dialog appears. Enter the p (paragraph) in the Selector field. Subsequently click the Formats tab and enter the 1 (or 100%) in the Line Height field. Click OK and subsequently Save to store this stylesheet rule.
On dragging and dropping the data field in the document a Text Script is created in the Scripts panel. Open the script by double clicking the script entry in the Scripts panel. Set the Format to Grouped. This will set the thousands separator for the string based on the current locale.
You might want/need to change the Locale to apply the separator according to format parameters of a specific language. To set the Locale for your document choose: Edit > Locale… The Locale dialog appears. Change the Use field from System locale to Explicit local and select the Locale required for your document. Click OK to confirm the setting.
The selected value is stored with your template and therefore travels with the document when publishing it to Workflow.
Setting the Locale might also be the solution for question 3.