Creating an online store.....total begginer, any advice please?

It will be sellig digital planners, meal & workout planners, gym t-shirts, mugs, caps......I have two jobs atm but am desperate to get out of the corporate world. I have a great guy building the site atm and he has some good marketing ideas's also. Anybody else who has been on a similar jouey give any advice for a begginer like me? WordPress ...