One of the problems with Yamaha's low-end keyboards is that they have no provision to recognize on-bass chords, which makes it hard to play modern music as written. Roland's entry-level boards always cost a bit more but had this feature. So does the tiny Korg MicroArranger (but factor in the cost of a full-sized controller.) A young/learning player should never be limited by the instrument so IMO, used is the way to go.
A young learning player.... should always start on a piano with a somewhat heavy touch... for training his finger muscles... its easy to move from piano touch to an organ, but not the other way around...
They don’t need an acoustic piano tough... a good digital is often much better then. Cheep acoustic.