Edit your map (data/world) with a map editor:
https://otland.net/threads/10-71-remeres-map-editor.211040/
You can find the teleport in Doodad Palette, Magic Fields. Then right click on the teleport, properties and there you can set the position it should teleport to.
You can add monsters with the Creature Palette, add a spawn and place the monsters in the spawn.
In config.lua you can change the exp rate, for specific monsters you can change the exp in data/monster.