A primaris psyker should choose the
CCS discipline, with 4x melta or plasma guns.
Al'Rahem is a delivery system, so pick what you want to deliver in a flanking position. Usually this means 4x melta on his command squad, and infantry squads that can hold objectives you wouldn't otherwise be able to reach. Chimeras can be very useful, but I would give the Chimeras to non-outflanking units first if you have a limited supply of them since the non-outflanking units have a longer distance to move to get anywhere. The main thing to watch out for is the cost of the unit, if you have too much of your army off the table your opponent can focus on your on-table forces and wipe them out before Al'Rahem can arrive.
JohnnoM wrote:2. He can't do hes special thing if they are in vehicles, have to be on foot only.
Wrong. Please read the rules for outflanking before posting.