good start!
I think it is a good start to the slow movement of a piece. I don't know if you are going strictly for the Concerto format, but I could definitely see this as a solo piano work. I wonder what a little experimentation into maybe splitting up block chords might aid in your work here, but if you are happy with the ostinato you set up, then by all means stay with it.
On subsequent listens, I think you could replace the arpeggiated left hand entirely with the string parts you used as the harmonies that the strings have that you set up draw my attention a little more than your ostinato left hand. Throw some pedal in there to help add a little haunting flavor and you got yourself a slow movement to a bigger work!