Since every update will involve new units and new content of some sort, they are not savegame compatible.

1.0 is also not the last release. There are plenty more things that we have planned that will go into the next version(s). However, 1.0 is a major release and it will be 'complete' in the sense that there are no obvious gaps that need to be filled. It might not be perfection yet but it will be a very solid release.