Headspace and purging for 12L wine kits

I’m thinking of doing some icewine and port kits. I’d primary in a 5G bucket, and then I’d like to age them in 6G carboys (it’s all I have). If I don’t mess with it after I transfer and don’t degas until I’m ready to bottle, will the offgassing during transfer to the carboy provide enough CO2 for the headspace, allowing me to keep it in the 6G carboys until I bottle?
Additionally, I have a kegging system for beer. Could/should I purge the carboy and headspace with CO2?