A simple NAS is a nice way to begin in the proper network storage environment where all computers are saving business data to a central protected location instead of on their own individual workstations. However, not all NAS, nor servers, are created equally and it's worth it in the end to get something high quality and do it right to begin with. Synology is a great enterprise brand, they're more expensive than some, but they're also more powerful and reliable.
One thing to keep in mind is a NAS will ONLY store files, you can't really do much else with it. If you want more flexibility and customizability, the next step is to look into a file server. Servers act similar to a NAS, where you can store and share out files, but generally are built using the same kind of hardware as your desktop computer making them more powerful, more versatile, and usually running the same or nearly the same operating system so it can be very intuitive for people to set up and well documented online for help. A server also gives you the flexibility to perform additional tasks if you so choose, such as running automatic backups, network printer sharing, email, FTP, web hosting, firewall/router, etc. It can be much more versatile of a system because it's running a full function operating system on standard computer hardware. This also means that replacing or upgrading hardware in a server is a lot more feasible than a NAS, which is basically pre-configured and offers no means for replacing faulty hardware or upgrading the base configuration hardware.
A basic file server, such as the HP ProLiant ML110 G7 server that we have used a ton of, can be configured and ready to go for around $1,500 when you figure in your hard drives and operating system, but can go over $2,500 when you start adding in more powerful hardware and fault-tolerant capabilities that far exceed your NAS systems. Most of the server systems we have been setting up are in that higher price range, but they include a hardware-based high performance RAID for data on enterprise class hard drives, dual redundant high efficiency power supplies, a very powerful quad core processor, and anywhere from 8 GB to 16 GB of RAM.
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