Start down when you fancy it.
Ummmmm, no.
The wind aloft is going to change as you descend,
It is. But the 3:1 works extremely well to get you started and the wind corrections make is even more accurate. The corrections you then make as you're checking your profile every few thousand feet are small.
but have a stab at it.
Again, no. There is no "stab at it". There are RoTs that get you very close to profile.