Like Ryu said, it is NOT a good idea to use as internal storage. That can cause all sorts of issues, and the day your ssd or usb connection get's flaky, it will corrupt your whole box and be forced to do another factory reset. Format it as portable storage and it can be used for downloading movies, recordings, etc.. as long as you set the options accordingly int he PVR options section.
And as a test, IF it is possible, if the freezing persists, try to run an ethernet cable from your router, to the box, to eliminate the possibility that it is some sort of interference with the wifi causing the freezing. Does your router only show a single SSID and handle band steering internally, or does it present 2 SSID (one for 2.4Ghz band, and one for 5Ghz band) where you manually can select the one you want ? Very often many routers can cause glitches in the way they try to do band steering and sometimes constantly try to renegotiate back and forth between both bands. You are better off, if possible to disable any automatic band steering and ideally be able to manually choose a 2.4 or 5Ghz SSID.