Small Business Network Needs Best Possible 'archive' Hd Location

I need to add a larger hard drive to our network for archive access. I know just enough to be wrong on this, so I am reaching out for help.

We currently have 4 Mac Pro (2010 to 2012ish), 2 IMacs and one Mac Book Pro networked in a small office. Due to reconfiguration of the office over the past few years, one connects to a switch via ethernet, two others connect to a timecapsule via ethernet and two connect via wifi to the timecapsule. The timecapsule is the time machine for two of the machines; the time capsule is connect to the switch via ethernet, and the switch is connect to a comcast modem.

Currently, we have archive of design projects on an internal drive on one of the Mac Pros which serves as a sharepoint for others when they need to retrieve old files. It's slow.

So I want to add a 4tb external HD to the network as a sharepoint instead of the internal.

Do I add it to the time machine via usb 3 or do I opt for an NAS drive and attach to the _______. Switch? Comcast modem?

thanks

I would go with NAS device from Synology because with it many apps you could use with your business including a VPN server.