Start more at the beginning.
Who are you selling the posters to?
How are they reselling them?
What kind of stock are you envisioning using (some of the nicer ones are too heavy to roll and some of the really cheap ones tear when taking out of the tube)
How are you getting them printed.
Sometimes your print vendor will supply all kitting (packaging and shipping services)
How big are they? If flat have you considered how you would package them rigidly enough to prevent damage in shipping? The bigger they are the harder that is.
Are you considering “archival” inks and papers? (often called giclee printing but take that with a grain of salt.) That determines where you buy your packaging and what kind of plastics you use (so does the inkset, some inks will stick to the insides of some plastic sleeves.
Of course you charge for the packaging
And for the shipping
You are out to make money right???
My consulting fee will be in the mail.