Hi Gimper,
Thanks for the feedback.
The default to shoreline is simply because there can only be one shoreline, but possible many islands. We have users with over 100 islands in a single map project, and if they are all imported at once then changing those back to island (from shoreline) is a lot more work than changing the single shoreline. I agree that it can be confusing, especially when you have just a shoreline, and we could probably think of a better way to do this - perhaps an option during import as to what the default should be.
A Workspace can hold any number of projects, and also other other stuff, such as tracks, user maps (edited maps) and waypoints, which aren't themselves members of a project. It does add another layer of complexity, and I know its not the way that other mapping programs such as DrDepth work, but it is also quite a powerful difference.
I think once you get familiarised with the ReefMaster workflow most of these things will become second nature, and it sounds like you are getting there!
Matt