Generally if you do not want city, zip/postcode level rules, you do not need to purchase additional geo location.
In case you have to purchase, you have to purchase for entire Africa, however, while uploading you can opt to import only your country data.
yes, you can setup free shipping based on city. currently, yes you can filter products by free shipping
We can send you sample data on your email, how it looks like. you can anytime rename the zip to postal code by language translation utility.