Hi and welcome.
Become as knowledgeable about your product as possible-- this board is a good place to start.
Take a look around your area at other shops to see what they're selling, AKA what they're customers are buying.
A big inventory can kill you, and you can't be all things to all men unless you're made of money. Chances are, you're going to sell a lot more Spinner batteries than $300 custom rigs. It's OK to have a few in the display case for the customers to drool on, but don't bet the ranch on selling a lot of them.
The real money is in the consumables: wick, wire, disposable cartos, coils, juice, etc. Keep a good stock of those. Learn how to DIY your "house juice" and make it tasty and top quality as reasonably as you can set the price. Another option is to find a local brewer who's willing to work with you on it, maybe make you a custom blend or two, or put your labels on, etc. You'll also need some "gourmet" juices from national manufacturers, but hopefully not a lot.
Be careful about whom you hire: you don't want teenage kids who sit in the lounge and blow cloud with their buddies to the point they won't wait on the customers or talk to anybody who doesn't have a 10 zillion watt mod.
If possible, put you "tasting bar/vape lounge" away from the bulk of the customers. You're gonna get some cloud fiends in there, and the tootle puffers don't want that atmosphere.