the gershwin rhapsody in blue is a great piece. but also incredibly difficult. yeah big time.
the 2nd rhapsody is very much ignored and i think it is actually much more interesting, probably better than the famous 'blue'. i have not looked at that score in ages but i would be shocked if it is not as hard as the first, heck maybe harder.
really, i applaud your enthusiasm, but i would most definately avoid the 'big standards' the first time (perhaps 2nd too) around.
i only menitoned the warsaw becuase you seem to like that sound so much, but be warned i would not put it in the 'easy' category, definately not the hardest work out there but if i mainly mentioned it becuase of it's relatively short length, it's pretty easy to memorize (if you memorize pices well generally, if not, forget that statement). if you do not have a solid technical base it could be problematic for you (ie you can already handle very fast argpegios , i mean really fast, all up and down the keybaord, really good voicing, control, etc).