There are certain CSS classes for each question type so you can surely use those to adjust the font size for certain elements of a certain question type, see:
docs.limesurvey.org/The+template+editor&..._of_question_classes
When changing the template.css file, always do a complete page reload when checking your changes, otherwise the old, cached CSS file content might be loaded.
If you are looking for professional and easy to adjust templates, have a look at
www.limesurvey-templates.com.
As for your update plans: better wait 2-3 more weeks, there are still some issues with the current LS 2.0 code.