Questions related to the webpagetest notions

Hello forum,

I find that webpagetest is a really excellent way to profile the web performance and I’m looking for a solution to include the webpagetest results into a monitoring solution (like nagios, zabbix, etc).
But I cannot find some answers to my problem either in documentation nor in the forum threads. I hope you’ll can help me to see more easier how can I implements my goal with this solution.

First, I cannot really understand what is behind the private instance notion?
Does a private instance is a dedicated webserver which does the same thing than but is restricted to a closed public?
Or does a private instance is a dedicated monitoring location which is not listed in the test location map?

Secondly, even if the list of locations available for running tests is very amazing, I would like to add some additional test locations. What is the requirement for setting up a new testing location? I’ve seen that new testing locations are added by configuration in the private instances, but I suppose this is not the only thing I have to do If I wants to add a new testing location.
For example, if I wants to be able to view the performance of my website from Russia, what do I need to do?

Thirdly, does the testing locations availables from the website are available for anyone? Or does these testing locations can be used only by the website? And in case they are available for everyone, are there some restrictions to access them ? (delay, number of hits per day, etc)?

Finally, from your own experience, which is the average delay of executing a test script? When we launch a test from the website, we are put in a queue. If I run a private instance, is there a delay before and after running the test? I would like to know which kind of frequency I can schedule if I plug this software into a monitoring tool.