They are placed where they are to maximize the actual visible play area.
For your mouse you may want to in Windows choose Settings, Devices, Mouse. Additional Mouse settings. On the Pointer options tab increase the Pointer speed.
And why would you rightclick to change neighbourhood? Leftclick the neighbourhood you want and select travel here..
800x600 is a very low resolution and is why items in build mode appear so large for you. The resolution should be at least 1920x1080.
You use leftclick to enter Manage worlds.
Also you might want to learn the keyboard shortcuts such as F5 for Manage Worlds
