On the subject of the three-wagon multipack, I'm sure there are economic reasons for doing it in threes, but it will risk putting off potential buyers who might only want one or two wagons, and who might balk at shelling out over 100 Euro just in order to have the one. It also potentially creates a profiteers' market on eBay. If profit is to be made (and there is little of that in railway modelling generally), it should be made by IRM, not eBay sellers.
It's massive growth, because it starts from a fairly low base. Any growth in Irish railway model availability is to be encouraged, but we should all make sure it's not a false dawn.
I'd hesitate to call it a Golden Age, though. That sounds like hyperbole. A few extra swallows don't make a summer.