In an production/office/business Network, STP is enabled by default, especially on Cisco switches. Is your Network involved with the Above? If not, you should not be in a position to utilize STP.
http://www.ubnt.com/edgemax#edge-router
$99. Can't beat that price for Performance. BTW, watch their Promo-videohttps://www.youtube.com/watch?v=M2QSHLdJ-s8&list=FLccmrXqDJIfBx_I2gaLo2TA&index=4&feature=plpp_video
I was once in your situation - got myself a QNAP TS-669(6-bay), freakin' loving that unit. Before entering that realm of devices, do check the "compatibility" list.
Look into QNAP or Synology Servers, for Folder structuring and Permissions.
QNAP does have a few Apps that allow a specific User to access Folders & Files - presuming all Users are utilizing IOS devices.