I should make several Quickbook accounts for my clients. Can I use only one of my email address for several Quickbook accounts?

Welcome to the Community, usa_tax_consulti.

Let me share some information to help you choose the right region for QuickBooks Online.

Yes. You may use one email address for several QuickBooks Online account. Most of the time, the region will depend on the company's location and where taxes will be paid.

I've added this page so you can check the Plans and Pricing for QuickBooks Online.

Once you've sign up for a US QuickBooks Online account, use this link to check for helpful articles: Getting Started With QuickBooks Online.

Don't hesitate to post or leave a comment below for follow-up questions. I'll be here to assist. Have a great day!

@usa_tax_consulti 

If your client's company is located in the US, you should pick QBO US version.

https://quickbooks.grsm.io/US

https://quickbooks.grsm.io/us-promo