I almost cannot believe this coincidence. Yesterday I spent almost the whole day to create a multiplayer top down shooter with waves of enemies and RPG elements that is working quite nicely (my first multiplayer that works, too). If I deactivate player movement acceleration and make smaller waves it should work nicely via internet, too.

(I know that it looks shitty, there is only one player visible, the rest are bots.)
That means I would like to play such a game and I will follow your development with interest.