Thanks for your interest with our services, @qbtaxconsulting,
At the moment, global version of QuickBooks has a limitation with the number of users who can access the company file. The Plus version is set to allow 5 billable users and 2 accounting users.
Here are the user types you can add to your account: Master admin, Company admin, Standard, Time tracking only, Take payments only, and Reports only.
See this link to get more information about user management in the program: User types and user permissions in QuickBooks Online
Otherwise, if you're referring to adding unlimited company files, you will need to sign up for a new QBO account for each business. Every company you will add will require a different subscription and a separate billing.
To find the version you want, click this link and choose your country: Choose your country for QuickBooks
You can also use Fiat Lux - ASIA's link to sign up.
If you have other questions related to our subscriptions or anything QuickBooks related, feel free to add a comment below. I'll be glad to answer them for you. Have a good one!