I talked to Janne today. He fears my insulation order of 300mm thickness in the roof and floors is way too much. He has only 100mm in his house, and most of his builds have only 195mm. Physically, I've ordered a lot of insulation, which has to be shipped and moved. Janne said he's worried about my back and my budget, and I appreciate that! Wille also said most of his houses have only 195-210mm too.
Plus, the walls aren't insulated, so it seems silly to have a lot more in the floors and ceilings than the walls. It's like wearing a ski hat and gloves with a T-shirt. And I have to remember this isn't a year-round house.
On the other hand, we have only the one chance to add insulation, and Willie brought up the possibility of an echo, or drumming, in the floors if we don't fill up the floor void, and leave a hollow space underneath.
I'll try to talk to Stefan in the morning and see what he thinks. At the moment I'm leaning towards the full 300 in the floor and 195mm in the roof. I'll report back.