Don't worry to much, that's still beginning (period of tests, etc..) for the game. I'm sure with future updates will came a day when unit cap will be incresed.

Yes!

It would be great if some monsters appear at night and disturbe both teams a bit.

You could not prepare because they are reborn randomly and should not be visible on the map.
Of course, they should be weak, but to make them a more time consuming they should have more health and skills to attract or apply "fear" on our units.

That also open the possibility of necromancer-like bosses.