VIP Membership database via Wifi

Butcher shop (Meatland) wants to sign up customers to a VIP Program by WIFI and to to record their personal info into a database. Like how Calvin Klein does it in their stores. SEE PHOTO ATTACHMENT Customers will turn on their wifi on their phones (when within range of the shop) and choose i.e. named ‘’Meatland VIP Program”’ from their wireless network options . Then they will be requested to enter personal information ie. name ,d.o.b, phone number , email , etc (to be provided) ….then click enter. Upon clicking enter, the customer shall receive an email or sms to confirm they are registered. By doing so they will sign up to my VIP program and it will save me doing any data entry. I want the guest access to my wifi to be secure so no one can access any features of my network ie. my internet connection, printers etc. It is purely an open network for receiving customer details. Question: • Do I use the shops existing closed network Wifi Router which provides internet to my employees to perform dual function, or do I buy a new pc and/or router specifically for this task. My main concern is illegal entry into my private network via the open network. Please provide a price and a basic explanation of how you would do this setup, and maybe how you would improve my idea.