Welcome to the Guild Xeziares! As to your questions:

  • The map could be an island, or a continent, the scale is completely up to you;
  • Depending on the scale there is no reason why 4 kingdoms could not fit on the map;
  • Rivers are created via run-off from ran and snow, they flow downhill (seeking the lowest plane) from watersheds in mountains, they start out as small tributaries which join to form larger rivers, and eventually they flow into the sea. They don't generally split into smaller rivulets near the coast unless they are on flood plain. There is a sticky on the topic of how rivers work I believe in the tutorials section which would be worth checking out.
  • Swaps generally form from inlets near other bodies of water in low-lying areas with poor drainage. Since the water isn't moving very fast it just tends to collect.


Cheers,
-Arsheesh