Interesting concept! I'm curious to see where you go with it.
I put in the unit count total for you (two events, at the top of your main event sheet.) It includes both units in transit and units stored in the bases. The important thing is to remember that Construct processes the event sheet from top to bottom, so you can use stuff like 'add to variable', 'set text to variable', and 'set variable to 0' in the same tick. If you use a loop as well, then you can do something like 'add each private variable to global variable', 'set text to global variable', and 'set global variable to 0', resetting it so it'll add up again in the next tick.
The best thing about Construct is that implementing that concept is almost as easy as explaining how it works. Have a look at the events, and let me know if you have any trouble.