Hi polarbear ..yes a 30 gal is way too small for an oscar ...they need 75 gals for one to be totally happy...their waste is huge and their body size is as well....plecos are just as bad as oscars...they produce too much waste for that size tank....you could keep a juvie oscar in a 55 gal, but within 2 years you would need a 75 gal just for the one...and in the 55 gal, you would need extra maintenance .....
the farlowella seems to be a difficult fish to keep from what ive read..and isnt for a new hobbyist or new tank..heres a link for you
http://badmanstropicalfish.com/profiles/profile57.html
I have a buddy with a fire eel and I swear that thing is almost 2 feet long...but im a girl and we kinda stretch things LOL but i know he is huge...I dont think the 30 gal would work for him either...