Hello there! Thanks for your purchase :)
About your questions:
- The side door/spikes are taller in order to overlap the top walls and give a better sense of depth (implying they are as tall as the wall, and thus the path is closed):
- Those two left-aligned wall pieces are just thin 1-tile vertical walls, like this:
Now that you mention it, I should probably also add right-aligned ones, and horizontal ones...I'll do that.
Let me know if you have any further questions!