Hi,
as mentioned in previous answers, the sooner you test the product the better, so I would recommend before doing the business plan, launching your website and social media running, as all of these need time and financial investments, which will be lost if the product fails the validation. As you mentioned, that the product is for university students living on campus, you should be able to validate the product easily on the campus. You can do also AB testing if you are deciding between 2 or more product options, to seen which option would be preferred by your niche group.
Wish you good luck,
Sabina