So one wave with at least one unit, preferably 2-3 (including a hero if need be) every six years. This is in addition to replacement of old kits in factions that need that to happen. This would mean factions like Kharadron, Fyreslayers, FEC, Ironjawz, Savage orcs etc would have a few extra sets by now.
I can't really comment on battletomes ghbs and campaign book because I don't play, but I would have the first out in the first two years, the second in summer and the third in the last four years of an edition.
In the infantry heroes GW presented this edition, it sort of feels like these were designs that didn't make the original cut that have been recycled, and they sell them for the price of 20 Frostgrave soldiers. I'm not into that.