Glad it worked out technically. Results may take some time. I'd really focus on sending high-value content for your audience and let nature start to take its course.
You might consider leveraging the Customer Engagement Engine, which is all about establishing a cadence, and makes it super simple to add content over time without having to worry about who already got what, where people are in the flow, etc.
Furthermore, the new Email Program with much easier A/B testing capabilties is something to investigate.
Mark's suggestion is somethign to work toward. The system part of that isn't that difficult. It's creating the content versions that can take the majority of time. Of course, sometimes that can also be simple, such as creating different versions of the subject line, or swapping a different case study depending on industry, etc., which doesn't take much time.
Good luck!
Mike
You can use a random sample work flow to break up your big list (Smart list) into the five smaller lists (Static Lists). The flow step you want to use is "add to list". Here is the documentation...Key thing that is hard to get the first time doing this is that you need to create the five emply lists and then populates them with a smart campaign.
As far as your out-bound campaign just use wait steps inbetween the send email flow-steps...