* I ran a 'full paths' report to find the bulk of the paths involving that particular page is only approx 4 pages, yet when I run an average page depth report for that same page, its telling me its 12 pages.

Answer:Full paths report are unique paths on a site a visitor generally takes. However average page depth tells us how deep a page lies within a visit.
Both are different as in SC (analytics and reporting) it gives all the possible paths taken by the visitors.Hence to better understand the importance of a page, it will be better to use Pathfinder or fallout for that particular page, which will tell us how many of our user drop off and where from that particular page. 
Whereas in full paths reports there can be numerous (atleast)  of unique user journey comprising that particular page.

* The full paths report tells me in the bulk of the journeys, this particular page is where the user exits from.  However, when I run a report on 'exit %", its only approx 20%? 
Answer: Same as above, it will be better to try fallout report to understand the drop offs and exits from that particular page.

* Also, is there any way of running a full path report that isn't limited to the max of 8 pages?
Answer:In sitecatalyst it is limited upto 8 pages.

Hope this helps. Please mark as solved if this resolves your issue.

Thanks for your reply, I'm still a little confused sorry...

What I am trying to understand is how do users get to the first page of the cart journey, where do they start from and which pages do they visit prior to the cart.  Which are the best & shortest journeys, which are the longest journeys. So based on this, which is the best report do you think?

I still don't understand "Answer:Full paths report are unique paths on a site a visitor generally takes. However average page depth tells us how deep a page lies within a visit." - to me the page stats should still match, can you please help further clarify?

thanks again.

Lets understand it with an example:

Different visitors came to your website.

Visits for different pages (A,B,C,D)
1) A> B>C>Exit
2) A>C>Exit
3) A>C>B>Exit
4) A>B>Exit
5) A>C>Exit

So if we run a full path report all 4 paths (except 5th one which is similar to 2nd one will be counted as 2 visits) different from each other will appear in my report. 
So full path report will give me all the unique possible paths user has taken to navigate in my website.

1) A> B>C>Exit     -----1 Visit
2) A>C>Exit         ------2 Visit
3) A>C>B>Exit     ------1 Visit
4) A>B>Exit         ------1 Visit

So there could be many many possibilities for user to take and hence many paths will be reported in full path journey.

how do users get to the first page of the cart journey, where do they start from and which pages do they visit prior to the cart.
Answer: Try Fallout and Pathfinder analysis

(Reference: http://blogs.adobe.com/digitalmarketing/analytics/pathing-analysis-inside-omniture-sitecatalyst/  )

Which are the best & shortest journeys, which are the longest journeys.
Answer: That is quite an elaborate question which depends upon your KPI's, nature of your website, business goals.

Thanks for your reply.

So in your example, the average page depth of Page B (1+2+1/3) is 1.3 right?  What I guess I don't understand is how/why this metric can be any different to the pathfinder/full paths reports?

re: Which are the best & shortest journeys, which are the longest journeys.  What I want to understand is which are the shortest journeys users take to get to the cart, and which are the longest journeys (& whether this can be optimised upon).  What we want is to get users to the cart as quick as possible.