I am using the widget, and was wondering if it is possible for my homepage to display a map (in the widget) displaying all locations/posts, and interior pages/posts displaying the map of that particular page/post.
Secondly, I’d like the interior page/post map to display markers of posts nearby, if they are viewable on it’s map.
In reference to your first question YES, you can create separate widgets for different pages.
I use the plugin ‘widget logic’ for this purpose. It’ll give you a conditional field so you can say “show widget A for the main page, but widget B for all other pages”.
For the second part: the plugin itself doesn’t have a ‘show nearby posts’ function. But you would need to come up with some criteria for ‘nearby’ posts – perhaps you could all posts in the same category and then zoom the map in to show only a 5-mile radius around the original post?