2) Personal opinion, but I'd prefer you to not to say anything* until you're given a marshalling instruction past the Holding Area entry point (LOKKI, ETTIV, OSTER, etc). If when you receive that marshalling instruction, you still are not ready, then say so at that point. Gives us a chance to re-plan, but doesn't defeat the purpose of 'monitor tower.....'
*...if it's going to be a few minutes. If you're expecting an unusually long delay, then I'd recommend telling Ground when they pass you over to Tower.