Great Idea.  I'm working on a series all about action cameras soon.  I'll put a section in there about technical specs and ways to approach more compressed footage that you typically get from action cameras.  

I reuse clips all the time.  I think theres no issue in reusing b roll.  I actually built a stock library of my own footage in a FCP file so that I can search and find clips fast.

Check out this video.  it has a few more tools for video ideas.  Also VidIQ has som good tools for video ideas

What you're trying to avoid is if that dip stretches much further to the bottom which is called the hockey stick.  

Looking at your retention graph that is normal.  For my main channel tutorial style videos theres always a dip at the front like that.  Here is a recent video and you can see I have a similar dip. You can see the grey is my typical video so this is performing normal for me.

Theres a feature to upload photos here in the community.  Go ahead and upload the photo here so we don't have to link out to see it 

Look at what happens at those dips.  Did you say something or did the video slow down?  Use the dips of a guide on where to look and see what happened to cause people to leave 

Jonathan Richey Good idea.  You can add in all your social channels to get a big overview of growth of your brand overall

Jonathan RicheyTake this and customize it for your income and expenses.  I like this format because I see a quick overview of everything and I can see whats working or not when it comes to income sources 

Here's a link to it: https://docs.google.com/spreadsheets/d/197HdKDn7aTz4lXbTrrLxcO5koG4jQn2G_RGjkBNBmCo/edit?usp=sharing