I would suggest a VPN concentrator at the office, with all other PCs / laptops having VPN client software installed.
Wherever you are, connect securely to the office LAN and access services on the server as if you were directly attached to the office network.
Given the list of requirements (network connectivity, database, email, backup, Mac support) and your admitted lack of IT knowledge, you would be well advised to consult with an IT specialist to come up with some alternatives & associated costs and then implement the chosen solution.
SD