Can someone who has experience with gaming monitors help me pick one?

Standard monitors have a refresh rate of no more than 60 Hz. Gaming monitors can have refresh rates of 144 Hz or more. The standard 60 Hz refresh is known as the vertical sync rate (V-Sync), and all monitors support this rate as a default. The extended refresh rates of gaming monitors use one of two different monitor technologies, which are incompatible with each other. If you have an Nvidia video card, then you would need to use a monitor that supports G-Sync (Nvidia's proprietary technology, i.e. GeForce Sync). If you have an AMD video card, then you would need to use a monitor that supports FreeSync; it is AMD-developed, but made available for free and standardized throughout the entire video industry (except at Nvidia, of course) through the VESA consortium, also called "Adaptive Sync" by VESA.

There's no advantage of FreeSync over G-Sync, or vice-versa, they just achieve their similar goals with incompatible electronics. Because the FreeSync technology is standardized by the video industry, you can expect that FreeSync monitors will be cheaper than G-Sync ones, and that you can eventually expect to see even TV sets supporting FreeSync. Now that's not to say that a FreeSync monitor won't work with an Nvidia card, nor a G-Sync monitor won't work with an AMD card, they will however fall back to the old-fashioned V-Sync 60 Hz standard.

One thing to note though, Nvidia has a confusingly named feature called "Adaptive V-Sync". This is not the same thing as VESA's "Adaptive Sync" (aka FreeSync). This Nvidia technology simply stays within the 60 Hz maximum rate of standard V-Sync, but does a little bit of on-the-fly adjusting within this rate. 60 Hz is the maximum rate of V-Sync, but sometimes games can drop below 60 FPS, and during that time, you'll notice stuttering. So Nvidia adjusts the V-Sync down to either 45 or 30 Hz, to avoid this stuttering. But it doesn't go above 60 Hz ever with this technology -- you need G-Sync for that. Nvidia uses this technology, if you don't have a G-Sync monitor.

Does 144 Hz make a difference over 60 Hz? Current thinking goes that the human eye can only see between 25 to 30 Hz on average. So the 60 Hz standard was chosen because it's twice as fast as the human eye, so any sort of fast flitting movement on the screen will have been covered off by this extra speed. But of course, it's looking like the human eye is a bit more complicated than that, and it can notice flitting motion even at these extended refresh rates above 60 Hz. Gamers say that they do notice the difference between 60 Hz and 144 Hz, and even some of the newest monitors are going upto 244 Hz! I doubt that anyone is going to see a difference between 144 Hz and 244 Hz.

BTW, to show you how much cheaper FreeSync monitors are vs. G-Sync, here's a FreeSync monitor with nearly identical specs to that G-Sync monitor you have shown above. But it costs only $439 vs. $760 for the G-Sync.

https://www.amazon.com/Acer-XG270HU-omidpx-FREESYN...

I would say that if you plan to keep with Nvidia then you should get the G-Sync monitor. The GTX 980 Ti is still a very powerful card. If you have any plans to upgrade in the future and go towards an AMD card, then the FreeSync monitor would save you a lot of money. AMD's upcoming VEGA video cards should be a worthy upgrade for you.

get your friend to explain to you what your graphics card is capable of.

example: the MX27AQ isn't very useful if your graphics card can't support 2560x1440 at 60 Hz

Yes someone that's experienced can help you as Spock already pointed out a graphics card will be needed also possibly a new power supply or a motherboard etc. It's hard to tell without full computer specs.