Would this UPS suffice for my Gaming Rig?

Since your selected UPS outputs simulated sine wave, you might want to rethink your option and go with true/pure sine wave UPS instead. Here's further info about it and UPSes in general:

Good UPS brands to go for are CyberPower, TrippLite and APC.
Note: The more powerful UPS you have, the longer UPS can keep your PC running before it's battery is empty.

When looking for an UPS, there are 2 things to look out:
1. Output waveform (square wave, simulated sine wave and true/pure sine wave)
2. Design (stand-by, line-interactive and online)

From here you can read about the differences between output waveform,
link: http://www.minutemanups.com/support/pwr_un10.php

And here are explanations about the UPS design,
stand-by: http://www.pcguide.com/ref/power/ext/ups/typesStandby-c.html
line-interactive: http://www.pcguide.com/ref/power/ext/ups/typesLineInt-c.html
online: http://www.pcguide.com/ref/power/ext/ups/typesOnLine-c.html

Waveform and design
For PCs, line-interactive UPS would be more than enough since PSUs can easily handle the 2ms to 5ms transfer time of line-interactive UPS.
As far as output waveform goes, true/pure sine wave UPS is best used. While simulated sine wave UPSes are cheaper than true/pure sine wave UPSes, PSUs with Active PFC aren't compatible with simulated sine wave. You might get simulated sine wave UPS running with Active PFC PSU but there can be some major issues. Here's what, how and why.

How do you know which PSUs have Active PFC and which ones don't?
Simple, every PSU that has 80+ certification (e.g 80+ Bronze or 80+ Gold) has Active PFC.

What is Active PFC?
Further reading: https://en.wikipedia.org/wiki/Power_factor#Power_factor_correction_(PFC)_in_non-linear_loads

What can happen when using simulated sine wave UPS with Active PFC PSU?
When simulated sine wave UPS switches over to the battery power, one of 3 things can happen:
1. UPS displays error resulting PC to shut down immediately.
2. UPS shuts down resulting PC to shut down immediately.
3. UPS switches to battery power resulting PC to power off from UPS (PC stays on).

Why it happens?
Simulated sine wave UPS produces a zero output state during the phase change cycle resulting in a power “gap”. This gap may cause power interruption for active PFC PSUs when switching from AC power output to simulated sine wave output (battery mode).

What to do next?
As stated above, your PC can run off from simulated sine wave UPS but be prepared when you face issues with it. When issues do rise, your best bet would be returning the simulated sine wave UPS and getting true/pure sine wave UPS. Or you can go with true/pure sine wave UPS off the bat.

Wattage
As far as UPS wattage goes, you need to consider the power draw of your PC and monitors. Maybe speakers and wi-fi router too if you plan to plug those into the UPS as well. Though, printers, scanners and other such hardware (full list on your UPS manual) don't plug to the UPS since their startup power draw is way too much for UPS to handle and you can fry your UPS.

Taking PSU's max wattage as a baseline is good idea since it will give your UPS more headroom and you can get longer runtime out of your UPS. Since your PSU is 850W, and if you add your monitor to it at 30W, you're looking total of 880W. Wi-fi routers don't consume much power. For example, my Cisco EPC3940L consumes 12V at 3A which means 36W.

So, 1500VA/900W UPS would be more than enough for your setup.

Though, it seems that you've underestimated the cost of a proper, good quality UPS. Since UPS'es job is to keep your PC running when there's blackout by supplying good and stable electricity to your PC, they also cost a lot of money.
For example, i payed €230 Euros for one of my CyberPower CP1300EPFCLCD (1300VA/780W, true/pure sine wave, line-interactive) UPS and i have two of them in use, one for Skylake build and another for Haswell build (full specs with pics in my sig). That makes ₱14.000 in your currency while your selected UPS costs only ₱5.300 (€87).
Since your PC is expensive, it's not easily replaced. Like it or not, if you want the protection, it's not going to be cheap. Though, if you want cheap and good UPS, you need to buy 2x UPSes; 1st the cheap one and 2nd the good one.