Renting a car is certainly the easiest way to get around and can be more economical than taking the bus. Shuttle buses are another alternative. Distances are very manageable; you can easily stay in the Annapolis Valley and do day trips to the South Shore and vice versa. The longest drive most people will do is the four-hour haul to Cape Breton Island from Halifax.
The direct route to most places will be on a 100-series highway (eg 101, 102, 103), which have high speed limits and limited exits. There is usually a corresponding older highway (eg 1, 2, 3) that passes through communities and has varying speed limits, but none higher than 80km/h. The Trans-Canada Hwy (Hwy 104/105) cuts directly across the province from Amherst to Sydney without passing through Halifax. Other backroads snake across rural Nova Scotia, usually numbered 200 to 299 when traveling vaguely east–west and 300 to 399 going north–south. You’ll find more potholes than gas stations along these.