It is possible to use this module like Xero. I would like to offer accounting system for small companies. Do I have to make new installation for every customer or its possible to do it with one installation where users can see only their own profile (account, entered data,…)?
Sorry, You can not use WP ERP -> Accounting system like Xero Accounting system.
In WP ERP each of the companies should have separate WP ERP installed to maintain their business under it.