Just wanted to report a big success, the strawberry buttercream was lovely, and the cake worked out well too. A big hit. No pictures, because it was eaten in minutes, sadly. I used some of my special stock of cake flour, and it was worth it. Must get a microwave and try the flour treatment experiments.
On a related note, I wonder if senior bakers have ever regularly used the creme anglaise buttercream that Julia Childe used to use in her early cook books. That used to be my favorite - not a as complex as the mousseline.