1. I don't believe a fish's growth can be stunted. A fish will continue to grow to its normal size or it will die trying. Small tanks restrict the normal development of muscles in a fish, which can lead to their death.
2. As it's already been recommended, an eel is not really suitable for an Aquapod, even if it's very small. You say you don't plan on keeping it forever, but we've heard that before, and it's really just hot air, no offense meant.
3. You can do a few cool fish in your Aquapod which I think will make you happy. A few great suggestions have already been made, so start with those and check out the fish profiles of the ones that have been mentioned.
In my 30G, I have two Black False Perc's, a Purple Firefish, a Highfin Banded Goby and a Clown Goby. They add a lot of color to the tank and each fish has their own personality.
4. Another suggestion for your tank, if you want the "cool factor," is to get a Mantis Shrimp. They are definitely "cool" and something different. However, it's not recommended you keep fish with them unless you're treating the Mantis to a special dinner