Far as I know all UPS are inherently surge supressors. So, wall -> UPS -> PC. I plug the PCs, monitors, modem, and router into the UPS side of the unit and things like printers into the suppressor side.
A run of the mill (roughly US $75) UPS is enough to give me plenty of time to shut down during an outage or hold the system a very long time in standby.
most UPSs have surge protection built in. and some UPS use the battery for Voltage regulation. an AVR won't protect you from power outages, and can allow a power spike through, but are much cheaper and can handle longer duration brownouts. if you have surge during a bownout, a surge protector may not block it, and i could get amplified by the AVR.
i would order things:
> AVR (min. watt for PSU watt or UPS VA, which ever is larger)
> surge protector (min. 600 Joule)
> UPS (min VA = 2xPSU watts)
any one of those can be removed, and the numbers are recomemended. but none should be less than the PSU rated power. (in a perfect world 1watt=1VA)
the AVR takes some stress from your ups, the surge protector absorbs the over voltages not adjust quickly enough by the AVR, the UPS protects from power outages (for a little while.)
again some UPSs will do all those functions, and cost more.
1KW wouldn't hurt but is overkill (to me at least). I run a 750W PSU on a 450VA UPS since my actual max system draw is right about that, including 20% PSU overhead. For me, the odds of a power outage during a full system burn test is remote enough to not be worth the extra cost (since I do that about once a year...). Had a couple of outages over the past year and all was well. Better to be safe tho if you have the cash.
If I add a second GPU, will certainly need to go up to 750W UPS.
more it can store, the longer it will output power duing an outage.
for example a cyberpower CP1200AVR has a 1200VA / 720W rating and a full load time of 3 minutes. you could get 5 or more minutes out of it. i forget the math for the VA to Watt conversion, it has to do with the way a ups converts DC to AC power. but i always considered 2x to be safe. 650W load x 2 = 1300VA rating. this will also give you wiggle room for forgotten/phantom loads. i always expect to have the display, network devices, and other perhipherals pluged into the UPS/AVR, but forget to count their watts.
also, just because your power supply is 650watts, doesnt mean your useing that much.