LOL. along with what SOOP NAZI AND ANUBUS SAID yes any bullheaad catfish is way too big for that tank. but if u like whiskeers soo much try some glass cats and cory cats, and maybe a few loaches. they have whiskers for ya and most of them wont exceed 5 inches. get a small group of those uand u will be set.
puffer wise, honestly i would wait if i were u and do a little more research on the puffers. they require more maintenance than u want to do and require specific water conditions as well.
i would get
3cory cats
3 glass cats
and 3 yoyo loaches NO more and not at the same time unless ur tank is fully cycled.
the corys, glass cats, and loaches, are passive fish but they have whiskers and they will do fine in ur tank.
if u want to get aggressive fish. i would strongly suggest getting a BIGGER TANK. say 60g++++
have fun

u gotta lotta thinkin to do. lol