30 Gal Freshwater Aquarium + Chiclid Question

Thinking about getting a cichlid. That statement alone probably
conjurs up many questions that you would need to ask, so let's see if
I can explain my situation some, so that I can get some advice from
"the pros".

I'm not sure which chichlid that I would like to get (JD, Tiger Oscar,
etc.) as I think they all look very cool. So far I believe I am
leaning towards getting a Jack Dempsey. On to my questions!

I currently have a 30g freshwater tank. It now has a couple of cory
catfish (1.5" ea), an argentina tetra (2+"), an upside down catfish
(2+"), tiger barb (2) and another small tetra (headlamp I believe)
that's managed to hold his own.

1) Will any of these fish get along in the same tank as the chichlid?
I was thinking that they would all have to be transferred to a
different aquarium (which I would still have to buy), but I was
curious if any of these fish would get along or if they've been in the
tank too long (2 to 3 yrs) with each other and should be all
transferred together?

2) Will this 30g aquarium be good enough for any of the chichlids or
should I consider buying a bigger tank for the chichlid alone?

3) Which chichlid is more interesting/fun/enjoyable (very opinionated
question I'm sure, as well as hard to answer, but I'm anxious to hear
anyone's response!)

4) What are some of the main differences between the Jack Dempsey,
Tiger Oscar?

5) Any experience or comments on the jeweled oscar?

6) Finally, not much time is needed with my current setup to keep it
clean and maintained. Will there be a consider amt of upkeep with the
chichlid?

Thanks!