In terms of customer validation it sounds like you have some but it hasn't been exhaustive by any stretch. Trying to get Adwords-generated revenue with such a small budget isn't going to prove anything either way. Articles written by people from Fiverr.com isn't much better.

Pound the pavement and find 20 people who have inventory management problems, email 200 people who you think are in your target demographic. Find out what they hate about inventory management and if your solution can fix their problem.