My two cents, based on the 4 shortscales I've owned and 1 that I've borrowed for a few weeks recently. Mind you, I don't play shortscales exclusively. I use a longscale in my band and only play my shorties at home for fun.
1: My muscle memory took some time time to adjust. The distance between the frets is not that much shorter, but big jumps still require looking at my fingers to make sure I land at the right one. I'm totally fine with that. There was one exception: I had a shortscale semi-hollowbody for a while that had a separate bridge and tailpiece that were very far apart (so much so that it took regular longscale strings), and the nut was pretty far away due to the large body. That one required my full attention to play!
2: Depends on the bass. The semi-hollowbody had a large maple center block and was very heavy, so it balanced well. My Sandberg Lionel balances very well too, due to the heavy ash body and the upper horn that reaches to the 11th fret. The Lionels with solid and aged finishes have much lighter alder bodies, but still balance well because of the strap button positions (but those are a few hundred pounds more expensive than the sandblasted ash finishes). My Harley Benton PB Shorty had a 3/4 sized body and did not balance well, and my Atelier Z Baby Z-4J is Mustang-shaped and has a slight neckdive but not too bad. The body is of very light ash and the neck is narrow but chunky so has some weight to it.