The answer in short to both, is yes you can, please follow the guide below to see how you can accomplish this:
Free Delivery over a certain spend ( Globally )
1. Whilst on your dashboard, hover over "business setup" in the main navigation, and click on the "edit site setup" option. [Admin: Dashboard]
2. Locate the Free Delivery section, and apply a numerical value to when Free Delivery is applied. Also remember to tick the Free Delivery checkbox otherwise your numerical value entered will not work. [Admin: Edit Site Setup]
Tip: You can also explicitly assign Free Delivery to a specific user group and or delivery region ( zone ) in this section.
Free Delivery setup explicitly on a product / option
1. Edit the applicable product [Admin: Products Manager ---> Edit Product]
2. Prices & Delivery Tab, choose the applicable Free Delivery setting [Admin: Edit Product ---> Prices & Delivery Tab]
NOTE: Always remember to run through a TEST purchase to make sure your revised / new delivery service is working ok!