I reluctantly concluded that I needed to plan in quite some detail. I've redrafted the route to stick to a high level course throughout, so abandoned just following Alte Via 1 and the GR5 and opted for my own route that keeps to the mountains as much as possible whilst taking in more summits. This lengthens the whole thing a bit and definitely makes it moire demanding, but it keeps the character of the route fairly consistent.
One thing is for sure, it won't go to plan! On bad weather days I'll have to change it, but it gives a reasonable idea of where I'll be and when.
The red sections indicate where I think there is a high likelihood of
not completing and having to shorten the day/abandon peaks. Yellow
translates to a medium chance of having to change plans and green means
I'm fairly confident of being able to press on regardless of weather and
how I'm feeling.