I think this is an excellent idea and should help towards building a real sense of Community. When I gram in similar circumstances I also add a paragraph along the following lines to try and ensure that Newbies do not use up their gram limit and also pointing them towards Scribes:

"I hope that you are managing to find your way around. If you have any questions, please ask. As a newcomer, your grams are limited so do not feel obliged to reply to this. You can, however, always send a gram to any Scribe who is online since they are there to help and the gram limit does not apply. They will be happy to help in any way they can."

Any other suggestions about what we might do to make people feel welcome?