Once again, read carefully...
He is interested in Praise and Worship styles, and songwriting. I think that the S900 is probably the leader in that style, and also its' 'songwriter' styles.
Another consideration is whether he plays guitar himself, or not... Once again, without a guitarist, I would recommend the S900. But he says he plays acoustic guitar, so possibly the drums or piano get more important. Maybe an E60, then.
Finally, no mention of wanting to play live, or needing a 'player's' keyboard, so the 'live' sound of the Roland's and Ketron's may work against him. The Yamaha's sound very compressed, CD-like, which might work better for demos...
So, to wrap up, the two I would have you check out would be the S900, for it's styles and polished sound, and the E60, for it's 76 keyboard and wonderful piano sounds, live drum sounds, and good MIDI integration. Both would leave about $400 over from your initial budget. If you don't already have a good DAW program, Cubase could be bought (at least the middle level) with the remainder...
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An arranger is just a tool. What matters is what you build with it..!