Can the instrumental be in another key? like a parallel minor, or a relitive minor. Or would that be to dark?

If you are currious about what is Psychodellic... I would add to what ManXcat's suggestions that, you also listen to Jimmy Hendrix, Jeff Beck (From the sixties and early seventies) Jefferson Airplane, The Yardbirds, & QuickSliver Messanger service. These might provide some examples of the kind of sound you are looking for. It could also provide a comon ground language for you to use when talking to the Guitarist, since they have probably listened to those artists.

Good to have you back!