You're very observant :)
1. We're experimenting with a 'timeline' of when you unlock things. This is only experimental right now and may very well change.
2. This is a list of your active and completed missions. Missions will unlock things like buildings and items, instead of being all available at the beginning.
3. That's the Terraforming button. At the moment it's a temporary menu that lets us change what a tile is (grass, clay etc). In the final game we want a more physical, direct way of changing tiles. So for instance, to change from Grass to Dirt you would dig.
4. That's your inventory. Yes there's only 1 slot now :) You upgrade to more slots by adding upgrades like the Backpack.
Thanks!