Disklavier

I am an owner of a Yamaha Mark IV Disklavier. I am interested in obtaining music/piano files to expand my piano's music library.

What are some suggested downloadable music file sites [or should I stick with only downloadables from YAMAHA although pricey]?

What transfer format would be most reliable and efficient [zip file to lap-top then burn onto disk? File transfer via WiFi from laptop to disklavier? Direct to disklavier from scource?]

I am particularly interested in piano jazz. Are Art Tatum piano files available anywhere that are suitable/compatible for disklavier?

I am a complete novice and may turn to the Yamaha dealer for some further training on how to fully use this fine instrument. any suggestions are welcome. ...Mike