We use a 4 bay Netgear NAS for pretty much the same thing & it's all straightforward / transparent. 4 bay because - 2 drives are for shared files on RAID 1 & the other 2 are for backup, again on RAID1, if it's only for backup a 2 bay would allow you to have RAID 1.
Netgear was chosen simply because all of the other network paraphernalia is Netgear & I image that most credible brands are fine. With some brands you can spec the drive size to suit at the point of purchase & some come with bundled backup software if that's relevant.