NAS for Time Machine for 5 Macs?

[Enquiries]

Although your site has been very helpful, thank you, I need a little more help.
I'm looking for a NAS purely for Time Machine back-ups for 5 MacBooks or iMacs.
We have cat 6a in walls, and most Macs are connected via ethernet (but some will be over wi-fi). Will soon be upgrading to a Unifi WiFi 6 APs and possibly and a Unifi router, but currently an ASUS router with unmanaged switch.
I don't want to over-spend on a NAS for this basic need i.e. Time Machine for 5 Macs.
Which QNAP (or other) would you recommend?
Thanks

[ed]

Yes, WiFi6 would help a lot. Otherwise, you would need to schedule time machine backups so that they are done at different times and would not slow down the network and a NAS itself.DS418 would do the job. But something with more LAN ports of faster LAN like 2.5/5GbE would help a lot. DS420+, DS1520+, DS453D, come with multiple LAN ports.I hope this helps.