Before the Sale

Hello! I've been interested in opening an E-commerce shop for a while now, and I finally have the time available to start.

I've chosen a monthly subscription service, with 3-4 products inside. The problem is, how do I proceed? First speak with suppliers and manufacturers in my country in order to ask for retailer specifications? How do I price my products in order to make profit? I am not certain about the mark-up.

If anyone has any type of beginner advice that'd be great!