I have a product idea for a very specific niche (university students living on campus). When does the product validation take place? before creating a simple business plan and a website? or after having the website and social media running?
Since your product is in a very niche market, I would start doing trials, and keep it simple.
When groupon first started they didnt even own the products they would screenshot things from the internet so do the same and keep it simple.
For social media campaigns, I just interviewed a founder who wanted to sell healthy snacks online, and he said they invested 50$ in ads and got clients even before they had the products. He even went out to the supermarket to buy nuts and pack them to send them to clients.
Now they have just raised 1 million and expanding in 3 new countries in Asia.
Best of luck