Setting up new computer and it wont take my email

Question

Hello, I run a small business with multiple locations and have a bunch of computers. I am no IT expert but do my best. I want to use the reception email address to set up this computer but when I enter it ******@ivmenow.com it says That the Microsoft account doesn't exist. Enter a different account or get a new one. When I click on Create a new one and enter that email address it says. You can't sign up here with a work or school email address. Use a personal email such as Gmail or Yahoo or get a new Outlook email. We use google email which that email is associated with. I don't want to enter my personal email because then it syncs with all my files. I want to keep these computers all separated because different clinics start having large file volumes and so when a computer gets old I want to be able to just set up a new computer and the correct backup restores on a new computer. Does that make sense and how should I go about it?