Hi Chris,
I am posting on a phone so ignore any typos.
First off what town or city will you be working from so I can recommend where to go.
Down sleeping bags are no problem at all if in a tent.
I don't have a gear list but below is what I used, the lowest temps (in my tent) was about -5c probaly about -10c outside.
I had to pack a week before my trip so I errored on the side of caution, I was also testing out some proper winter kit so pack was a tad heavy.
Pack.
Aarn Mountain Magic 55
Tent.
Hilleberg Soulo
Sleeping and insulation.
Exped Synmat Ul and half Z lite
20f quilt
Gooses feet down parka
Arcteryx atom lt trousers
Pati Micro puff
Shell
Montane quickfire event
rab bergen event trousers
I just have guests who walked in the door so must dash but Pm me tomorrow and we can chat :-)
Cheers,
Stephen