New to Linux and Setting up a Small Business Server

Hello all. I am tasked with setting up a server for a small business (10 to 15 employees) and want to use Linux as the OS. Details as follows. My needs are: 1. File server, personal space for each user and shared space for all users - Windows clients Right now there is no DOMAIN or WORKGROUPS 2. Internet Firewall 3. Remote file access (VPN?) for specified users 4. Print Server 5. Calendar, Scheduling (busy, free time) and Contacts sharing - Windows Outlook and Thunderbird clients My wants are: 1. Host Quickbooks data files - shared between 3 users 2. Eventually add a SoftPBX to his machine, probably Asterisk with FreePBX My questions are am I missing anything? What packages should I install and in what order? And most importantly how do I configure each? Should I install a BASE (HOST) OS and then install different servers in Virtual Machines? If this path is taken then what to use as the HOST OS and what services should be run together on each Guest? Any suggestion would be a great help and would be deeply appreciated. Thanks for the coming support.

URL: