Its not that inkscape is the wrong tool just that it has limitations. If your intending to work within them then its good at what it does. It would be able to do coastline and zoom in and you could add extra villages and mark up the map. If your going to add loads and loads of detail at the zoomed in level then you might find that it will slow down more and more. So its a case of what do you want. If you just want country and regional outlines plus markers for the cities / villages then it will be fine. If you want each road in the city and loads of buildings marked up and want many cities then I would consider something else. You could then still use it if instead of keeping it all on one map you zoomed down to the city marker then loaded that city as a new inkscape map all by itself. Then it would not have to deal with all the cities in one go. It sounds to me like it will be just fine and you should try it out. If you think your going to do it with inkscape then ask about here on that as well to see if people have made large zoomable maps with it and what settings you might need. I would think, for example, that you should start with a very large sheet of paper (like A0) when starting the map so that your well within the expected number range of the app when your adding small stuff.