Hello
I too have a planted 30gal! It looks like you have a low-light setup.
If I were you I would add some easy low-light stem plants if you go with puffers to reduce reflections in the tank. I have never kept them, just read that they get a little distracted by their reflections

However I think Amazon puffers would be great in your set-up, and enjoyable.
If you like community tanks I'd go with 12-ish tetras, plus one or two of the following...
perhaps odessa barbs (I like barbs)
gourami if you like them
dwarf cichlids (Bolivian Rams or Kribensis imo if you have hard water... soft water go with German Blue Rams or Apistos) if you like cool breeding behavior... not as "community" though
Sidthmunki loaches if you like loach behavior
small rainbows?
Or you could go river tank... if you were feeling ambitious a paludarium would be sweet as well.
Edit: As much as everybody loves the corydoras

I would suggest switching to sand if you stock them. The gravel can hurt their little feelers (and maybe feelings).