Seeking advice in the world of ecommerce merchandising and vendor management

I would deeply appreciate any advice in advance! If you work in a buying/merchandising/sourcing role I would love the chance to chat more in depth. I'm working on a business plan that will hopefully turn into a startup in the fall of 2018. Let's say you were starting your own ecommerce retail shop in the apparel space. Where do you find merchandise to sell? Do you seek out wholesalers and work out a buying arrangement? Attend retail / vendor trade shows? Rely on brands to come to you trying to sell you product? How do the products on your shelves make it there? I'm not interested in drop shipping and ideally would like to avoid Alibaba. Thanks!