Stain it to match the rock on the side and hire a landscaper to plan an installation. Is that a water hydrant around the corner? You might consider a water feature like a koi pond and pretty plantings.

Water needs to run away from all walls so be sure to correct slope. It can be subtle but it needs to be positive. If water runs toward any walls it will for a little "river" and start eroding soil at the wall.

A metal rail sounds like a good idea.

Planting a big bush and some groundcover in the "well" area seems like it would suffice. You need to create a comprehensive landscape plan and make sure everything is worked out, before you start doing anything.

Would put a waist high black metal fence from the house to the edge of the drop.

Find a half dozen or more rectangle shaped concrete planters. Then, add to the sloped area parallel to the front exterior wall of the house: rebuild those "steps" to create actual steps with a metal railing that matches the black metal fence then set a rectangle planter on each step.

Those steps and your wall need to be higher than the ground beside it to direct water away from the house.

In the nook itself, unless you you're going to face the side of the wall and steps with stone or brick to create a more "finished" look, you could paint that block with the dark gray concrete paint to make it visually stark, and plant grass and keep it mowed until you know how you want to use that space.

In the meantime, you could also add something not permanent such as concrete a bird bath in the center of the space or a tall post with solar light atop it -- something that matches your metal fence above it..