What's the end game for this and after the ending will we have to restart or will just continue on, and just start a new game if we want a different playthrough?

The game doesn't have a "end" right now and i don't plan to have one.

With that said... I do plan to eventually add major quest lines that can be considered the main "Goal", but when you finish you will get some strong bonuses and character, but otherwise the game proceeds.