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

Hi,
my name is Sabina, and I am co-founder of a multi-brand store. Are you running your store already? This is a very broad question to answer as I would need more information on the product you are selling. A good way to meet and address new partners ( boutiques ) is to attend fashion fairs with your collection of dresses. You should also do a research of who is your niche group and based on that look for suitable partners (boutiques) for you. Social media and partnerships with niche influencers are not only a way to build your brand but also a relevant reference for any boutique you want address. The best way to convince any store to list your dresses is to have a product that customers love :)

Hi,
we are running on Shopify. At first we were also hesitating due to their fees, but they are worth it. We just transfered few months ago our running store to Shopify. We did expect growth, but the transfer not only significantly increased our sales but dramatically lowered our marketing expenditures.