NAS Server, Active Directory, Firewall with VPN, and Web Cloud setup

Trying to properly configure setup of a local network server that is a Synology NAS with proper active directory or file user permissions set and secure firewall network setup. VPN is not a must but would be nice if you can set it up as well. Would be open to using the Nextcloud service or Synology Drive Server if proper configurations are made for team share folder and file access permission, especially to any of the cloudsync Dropbox directories that are attached to the server. Lastly, would like to have a secure way to share particular folders or data with customers for quarterly or year-end reports such as financials and other applicable data that are user specific.