Welcome to VU dude, and best of luck in ATL on your new endeavor. Best advice I have is find a market, cater to it, dig in and nurture it. It will take a while to get established and build a name but focus on your customer service and take care of your people. People will support you if you really take care of them. The vaping industry at large is known for bad overseas customer service and you can ask pretty much anyone here, they would rather spend a couple extra dollars on something if they know the people on the other end are batting for them. If you were to open a shop and not gouge people at a 200% markup, you could move more volume and likely fair pretty well. You will also get a little more business as a brick and mortar but online sales are a roller coaster and it seems feast or famine is the order of the day.
You and your pop will need to get knowledgeable on the subject and quickly and be prepared to put up some capital and burn some money (sometimes it feels literal). You are going to spend a lot of time answering questions for people who are not planning on buying anything or are trying to impress/test you. It comes with the territory so if you are not patient, you should start practicing.
If you dig up a map of your area, do some research of all of the shops and what they sell in a 15 mile radius, you can figure out what is moving in your area and probably do pretty good filling in gaps. If you find two shops that you are in between and they both carry the same product lines but different flavors, grab and carry the some of the stuff they have and pick up the stuff in the same product lines they dont have. That can be used to entice people bent on one or the other to come see you instead. You can sell them their regular stuff from the overlap in inventory and offer them something new.