This could be 1 of the best deal of digital portable pianos i can spot some how
http://www.zzounds.com/item--YAMP70
although absent of midi output, however i felt that the touch feeling is relatively good and priced the lowest too(ignoring casio px100)
Mind that it's a weighted keyboard and it can be quite difficult to get used to initially.. should cost around RM2700 i think..
for your "sticky" key question, keyboard operates in a way to prevent pressing too many keys at a same time for some reason, preventing mis-typing. A musically keyboard doesn't have to be so, however numbers of polyphonic will be the limiting factor.
I own a 64 sound polyphonic keyboard and haven't encounter any situation where my tone is cut off.
Possible to learn piano by self?