You have a couple of choices once you have a Synology. You can either use Time Machine (which will work as if you were on a Time Capsule and make an image Disk). Use one of the options on the Synology, like Cloud Station Backup or Drive (which would work a bit like Dropbox). You could also just mount a drive and backup your data with Carbon Copy Cloner, ChronoSync, Arq. You would NOT have to plug in your macs to an external hard drive to do all this. As soon as your mac is connected to the same network, be it with wifi or ethernet, you would see the Diskstation and would be able to mount your Share point to do the backup with the tool you want. I would still recommend having at least ONE clone of your drive on an external drive for each of your machine to be able to boot from those since you won't be able to boot from a backup on the Synology. HTH.