Help setting up ARD to access 24 seperate macminis at 24 seperate remote locations?

Please forgive my lack of networking knowledge as Im a Graphic Designer by trade, turned "IT" guy for the small business I work at.

Im trying to setup a "Digital Signage" solution for a client using Mac Minis and Keynote. The presentation itself is great but I need help setting up Apple Remote Desktop to manage the 24 machines I'm going to have, across 24 different remote locations across town.

Can I even accomplish this with ARD? Can someone help me with a simple step by step breakdown of how to do this?

So far I understand how to:

Set up "Remote Management" under system preferences

Set up Port Forwarding on the routers

In my research I keep reading/hearing about VPN's and Dynamic DNS solutions, but Im getting very confused. Do I need to worry about that?

Thanks for taking the time to read this. Any help is GREATLY appreciated!

Jesse