This is really cool. Unconventionally small 'tanks' are really fascinating to me, and they are a good bit more so when they have fauna in them. I hope this tiny ecosystem fares well, and that all the life in it thrives and is successful at existing.
I very much like your scape as well. It is whimsical in an outer-space sort of way.
What is a reasonable amount of shrimp to keep in such a small vessel?
For a container of this size with a sparse amount of plants, I recommend one RCS. If it is heavily planted, then I recommend two or three RCS. Nice thing about RCS is they are very durable, procreate a lot, are cute, and make good algae eaters.