Single computer with TallyPrime is adequate for your operations, the Silver edition is what you need. A ‘user’ in this context is actually a computer system.
This edition comes with all the features & capabilities including Tally.NET and services like Remote Access.
With Silver you can manage as many companies (business entities) and personal books of accounts as you need.
You can also create as many users as you need, and provide each with the appropriate level of security. Your only restriction is that these users will all need to access Tally.ERP 9 from the system on which it is activated (licensed).
Since Silver supports Remote Access as well, you can authorize access to your Chartered Accountant, who with his Auditors’ Edition of Tally Prime, can remotely provide audit, compliance and advisory services.