Yes..... simple is good........ after all, the lyrics should be easily heard and understood (especially if you're playing Christian music, you weren't clear on that.........????) Lots of really really complex music just detracts from the song. In rock music.... the most used sounds are probably B-3's (organs.... especially ones with rotary speaker simulation), Rhodes's (Electric pianos..... especially nice warm sounding ones), and pianos. Piano and Rhodes' playing techniques are very similar...... mostly he should be keeping a basic rhythm going..... especially if you play lead guitar (Not strumming, or rhythm.... but soloing and riffs). Have him work with "locking in" with the bass player and drummer. For the B-3 playing.... this is a lot more like the lead guitar's solo's and riffs....... play some little catchy melodic phrase now and then.... add some percussive bounciness..... and above all................. DON'T USE THE SUSTAIN PEDAL!!!! He probably already knows this... but organs have no sustain pedal..... his foot should be on a volume pedal instead.
Look for some books too..... here's an interesting sounding one
http://www.musiciansfriend.com/ex/sh...443?pid=940164 I don't own that one, and have never even seen it.... but it looks pretty useful. I have one called something like "Learn Rock Keyboard from the Masters" or something...... it's pretty good. Hope this helps.