If I have my success and action criteria already defined for emails, landing pages, forms, etc. and I am using these pieces of collateral in the parent nurture campaign, do I need to co-define success for these steps in the nurture tag or will they all work together to progress the nurture flow? I do recognize that I may be over thinking this, entirely.
So, a lead's status in the Nurture campaign is going to be completely separate from any other Program. If you have Emails and campaigns in one Program, and you use those in the Nurture Program, they won't necessarily change the status in either Program.
The stream in your Nurture Program is designed to be a "set it and forget it" type of thing. You add the content that you feel will nurture leads in whatever stage you're working with, and then you have the stream send it to them in a constant drip. You can define a Success status in the Nurture Program if you like, but this would not affect any other Programs.
John