Questions about Oscars

I am seriously considering going over to my LFS sometime in the next few
days, and if the same Oscar that I saw there today is still there, I am
going to purchase it, unless you folks can convince me that I shouldn't.
I currently have a 30 gallon aquarium that the Oscar can call it's
home. The fish currently living in there, three small Bala sharks and
three small Gouramis will be traded in. I have a ten gallon tank with a
cracked glass that I could raise crickets in, to feed the Oscar. And
there is a petro station nearby that sells frozen bait shrimp, as well
as other frozen fishing bait, to also feed the Oscar.
Of the Oscars that my local shop has, only the one that I want to
purchase is not an unattractive whitish flesh colour. The particular
Oscar that I want is one that is predominantly greenish-black in color.
And it seems far more alert and observant of the things that are going
on around it, than any of the others that are there for sale. Also, I
have no idea how to tell it's gender, but if I do purchase it, I think
that I will call it "Fred". Any help on the pros and cons of owning an
Oscar would be very much appreciated, as well as just how fast one that
is currently only 2½ to three inches long would outgrow it's thirty
gallon tank. Thanks.~Dean.