We are looking to initiate a few nurturing campaigns; however, we never have all the content upfront.
Is it possible to continually add content to nurturing campaigns during run? Any recommendations for starting to use nurturing campaigns b2c?
Yes. See Engagement Nurturing on docs.marketo.com. This is precisely what it was built to do.
As Josh said you can keep adding content to your nurtures, and just make sure you add it in the order you want it to be sent to your leads. If its new content I tend to add mine a the end of the stream to make sure everything is received by all leads in the stream as they work their way through.