No alarms or excursions in the night I am pleased to report!
We stayed there for a weekend as a present from the kids for our Golden Wedding. You can stay in the hotel (expensive) or self catering in some of the buildings in the village itself - we stayed in Angel Cottage which sleeps 6, but there may be smaller accomodation if there are fewer of you.
We thoroughly enjoyed the stay - you get a chance for some people-free photos early in the day before the gates open and again at the end of the day. The food in the hotel was excellent - but at a price - we only ate there the one night!
Portmerion is very convenient for the Ffestiniog Railway as well.
I would stay there again.