Yes, it can all be very overwhelming. It helps to break things up into price and category. Plain ego batteries, passthroughs, then variable voltage egos (Twists, Spinners, Winders, etc.) After that, the MVP, then tube mods and mechanicals.
The delivery devices should also be separated into categories: clearomizers (top and bottom coil) from plastic to glass, then carto tanks from plastic to glass, and then rebuildables.
It's nice when you can hold and touch things for yourself.
Juice bar is a must. If you mix juice for your customers at purchase, it's decent to let your customers know to let the juice steep for a week or two so that it will taste as close to the samples as possible.
As a consumer or a noob customer, let the clerks know. Be honest as possible when telling them how much you smoke so they can gauge what nicotine level to recommend. Also, try everything first!!!! Don't take anyone's word for it. A 2 pad marlboro red smoker might not be able to handle 18 or 24 mg nicotine, so try before you buy!