ETA: I'm going to update the consensus to this main entry for ease of reference. And it looks like whatever gets suggested first on this topic is likely to become the consensus.
The geography will affect many of the other issues, such as agriculture, fishing, tourism, economy, etc. I know a couple of these details have been touched on already, but I thought it would be a good idea to discuss all of it in one place.
- Number of islands: One island, period? One island plus uninhabitable barrier islands? One main island plus a few habitable small islands? A chain of several similar-sized islands? One main island plus a few little'uns.
- Shape: Is it somewhat round, or is it more long and skinny? What is the farthest you can get from the ocean? Main island fairly roundish.
- Ruggedness: Is it mountainous or flat? This affects agriculture, tourism, and transportation. It also affects...
- Coastline: Sandy beaches or cliffs? One main harbor, or multiple fjords? Low offshore barrier islands or deep open ocean?
- Longitude: Is it isolated, way out in the middle of the Atlantic? Or is it a short hop from the mainland? Which mainland--US or Europe? Closer to US.
- Latitude: This has a lot to do with... Subtropical
- Climate: How cold are the winters; how hot are the summers? When is the main rainy season? How rainy is it? Which is the greater danger--summer hurricanes or winter blizzards? Mild winters--no snow; wet summers--hurricanes significant.