Dave,

I can only recommend the instruments I know well, and the first one would be the Yamaha Tyros3, which has a 80 gig HD as standard.

You are then privy to a vast 3rd party support system for styles, generally free of charge, as well as being able to purchase styles from Yamaha's IDC network.

If you want to spend less, as cost(#7) is important to you, then a second hand Yamaha Tyros2 with a HD would be my second recommendation.

Also, you could consider a Yamaha PSR-S900 which does not have a HD but instead uses a USB Flash-drive, which some find more convenient.

The latter two still allow you access to great 3rd party support.

Ian