I'm new to the vending machine business but I've seen similar things in other businesses, since I work with internet marketing. And most of these things are really useless, so I am not sure I would go for it. If you think it seems reasonable, you should go for it of course but keep in mind that it can be all fluff and content copied from other sites etc.
If he really had a very unique system, he would write a book or something "bigger" about it, I think...
If you have the time and the money for the machine then go for it. Sounds like the location is OK. If you are buying the machine used then if it doesn't work out you can always sell it. Starting with a single location and a used machine is a good way to start.
Don't buy too many diet drinks. You'll find they expire quicker than the sugar drinks. So if you are running one location just be careful not to have too much inventory. Will take a few weeks to get it right but pay attention and you should be fine.
Great tips, thanks so much! I honestly had no idea about the Diet drinks. And thanks for the encouragement, it means a lot to a newbie in the business like me.