First you gotta ask yourself, do you feel lucky? what are you trying to solve for?

General file storage with backup somewhere?

File sync from mobile devices?

Getting calendaring to your own hardware?

Start with what your goals are, them look for solutions that QNAP can support.

As I mentioned my other comment, I prefer using a NAS as storage and use a server for managing services.

This way I have services isolated by functionality - one of my VM's is ONLY for file management. It provides the SMB shares, an http file server, and an SFTP service. All other services that require file access do it through that server.

Which QNAP nas? And which OS?

In general terms though, look for an Apps section in the settings, and install the Apps you want. You may find the choice limited by the OS, but once you reach that limit, you can migrate to a full fat OS on a separate device.