Hello, welcome to YC,
I think your list of needs won't be solved with a single keyboard :D
first, a concert electric piano, is made to play piano pieces in a live performance were its sound won't be replaced, almost like having a real piano on stage, (those tend to be heavy no matter if they are called "portable". Functions like midi controller, synthesizer sounds, or any other non-piano sounds won't be covered by this keyboard very well, and you cannot add those "ultra realistic" sounds on it.
A Synthesizer, is the one for the good sounds, but if you have those "good sounds" in your computer you don't need to spend on one, (the 88k synths are expenssive and heavy)
A midi controller is only the keys to play what you have in your computer, it won't work by itself.
If is only to produce, not to live performances, I think you need a midi controller, and of course, good software and libraries/plugins (but that would be within your studio only)
here you can check some 88k midi controllers.