Was going to hire a classical organ for my wedding for someone to play but it is VERY expensive so going down the root of a digital piano or keyboard - what is the difference and will he be able to play a processional and a recessional peice of classical music on this ???
Yes, he could, on either, but a digital piano methinks would hardly be suitable - its voices would all be 'percussive' eg piano, harpsichord, xylophone, marimba etc.
Any half-decent modern electronic keyboard will produce a very acceptable 'organ' sound, but make sure the player has some decent amplification and speakers.