Puffers could work, but then you'd be limited to bottom dwellers since they're so territorial....
Plus, any inverts in the tank would likely turn into food.
On the lotus, I'm pretty sure they get HUGE. Plus if the tank has a lid the constant condensation could make the floating leaves rot/burn. They do sell "dwarf" lillies for aquariums... That would work better IMO. Still have the same rotting possibility, but they're smaller and cheaper.
I have a lotus seed if you decide to do it. I'll trade it for some of your trimmings.
Do you like tetras? If so, then why not set up another tetra tank. Or other schooling fish like Danios. A tank full of Giant Danios would be interesting. (but I wouldn't do it. lol)
If not, there are several other dwarf cichlids.... Like what about Rams?
Or maybe a tank full of Badis Badis? I hear they are absolutely beautiful, and super peaceful. Unfortunately, that means they can be unable to compete for food, so nothing else in their strata...
But, badis badis and a few african frogs (completely aquatic) could work well, since they are both shy eaters.
Then again, why do you want frogs? Weren't you complaining about the loud noises the frogs were making in your pond? And now you want it coming from your aquarium all night?
I vote for a group of Badis Badis, because they're relatively large (dwarf-cichlid sized) but totally peaceful.
Add a group of corys and either a BN pleco or 4-5 ottos and you're all set. :)
A school of hatchetfish could work with the badis... but have to make sure the badis get enough food, and that the hatchetfish weren't food. Badis have tons of personality from what I hear too.
If you don't like that idea... Why not set up a biotope? Put a world map on a wall and throw a dart on it- then mimic wherever you hit. You're smart anough, you might enjoy a challenge. (If the dart hits ocean, throw again. Marine is overrated.) Your favorite plant store MIGHT start selling biotope packages soon... :p
But not that I'd know anything about that...