The unit says 'up to one hour of backup'. Note that ups backup times are stated in terms of half load. So for that 1000VA unit, you would only achieve 1 hour of backup (+/-) if the load were 500VA or less.
You need to add up the max power consumption of all the devices that will be connected and then choose a ups based on that. If you want to obtain the rated backup time, it will have to be half of the VA rating of the UPS. [You can convert Watts to VA - multiply watts by 1.4. If the power consumption is listed in Amps, then use 120 volts x amps to get VA].
Because your only goal is to shut things down orderly in the event of a power outage, you can get away with a lower VA rated unit as long as the total capacity of the ups is at least equal to the power consumption of all the connected devices; ie if all the devices consume 500 watts, you can get at minimum a 700 VA ups. You just won't get the full backup time stated - it will be half.
One other thing to consider. Unless the UPS is a true 'online' ups, its output will be a stepped approximation of a sine wave. While it won't damage anything (and for a computer it won't matter one bit), it won't be ideal for the HT equipment so you may notice a slight loss of quality in the sound - but given that its purpose is soley for temporary backup so you can shut things off in an orderly fashion, I wouldn't be too concerned about that.
