FreeIPA and Keycloak will give you directory management (LDAP and Kerberos), identity management, and single-sign on (OIDC and SAML) which if all your computers are running Linux as well, will give you centralized management of users.

You can then set other FOSS business management/productivity applications like NextCloud, Oodoo, Seafile, OnlyOffice, LibreOffice, CryptPad, etc. To use Keycloak as its authentication mechanism.

A lot of this will depend on what kind of work the business does.

You’ll also want to look into log management and SEIM for security monitoring, Wazuh, Graylog, and others. This is especially true if the business has any data compliancy responsibilities in the country this is in.

I think the general consensus for homelabbers is a mesh network – Tailscale and Netbird are the two most popular options

The Homelab Show was a good one, though they haven’t posted a new podcast in almost a year. Lawrence Systems and Learn Linux TV are the makers of it and have their own content as well