Terrain: Build in UDK. Need three tillable textures for it.
Water: Need to create shader in UDK.
Rocks: Three or four types to distribute around the level.
Trees: Two or three kinds of trees, need varying sizes.
Grass and small plants: Need long grass for use throughout the level, several kinds of flower type plants and some shrub type bushes.
Skybox: Sunny after noon time, interesting colours and animated. Add in some planets as well?
Research Tent: Tent, microscopes, boxes, crates, tables/work benches and cages. Modular?
Creatures: Four or five kinds of creatures, some in the trees, some on the ground.
Other: Sounds, particles lighting effects and wind effects!
All these should be the main requirements for my level, once they are all created fully and arranged in the level, it should hopefully look how I am imagining the level to be.