I'm certainly no expert either, but I'd tend to agree with what you both have been saying so far
It's nice to have some of the work done in the Autumn and some lilies can perform a little bit worse the first season if spring planted. It's also very true that an autumn planted lily can die in its first winter as it will be more sensitive.
My only suggestion would be to get the work with preparing soil and beds done in the autumn and then it will be very easy and quick to get the planting of more sensitive lilies done in spring.
