Small Business Network Setup.

Looking for some input on how to securely do my network, thank you in advance for any help!

I run a small restaurant, no more than 100 people in the building at our busiest, likely average 20-30 people per hour. Layout for my building is back prep room and office, then the kitchen, then the dining room, and then the front kitchen/register area. My connection is 100 down 4 up. My office is towards the back of the building, this is where my modem and router are. At the moment the only think plugged in is my credit card machine at the front of the building. We have no POS or anything that have to be wired. I have a private network set up here, and am currently using a Netgear ac1750 with a Mesh Range Extender to help reach the front of the building, though it doesnt work great on the other side of my brick wall.

What i'd like to do is have my private network for myself and employees reach the whole building while also having a guest network for customers. What do you folks think might be the best way to go about this? Ive been looking in to Ubiquiti access points, thinking that i can run 2 across my building from my router. One to the dining room and another perhaps on the ceiling of the front kitchen area.

I have no experience with guest networks, but i was hoping i could make this available to my customers with some advice/help from here.

Thanks again!