Based on your case preference, you'll be able to use any motherboard form factor. As for your budget, you'll be able to get a mid-range system. Addressing your concerns about 120FPS, I PERSONALLY feel that it's pointless to want to reach this FPS if you're only going to be using a 60Hz refresh rate monitor, which basically means anything about 60FPS is redundant. So, here are a few recommendations:
1) Case: Chosen
2) Processor: I would recommend you to go for an Intel-based system, since you are new to the scene and probably would like everything to work (almost) out-of-the-box. Intel has generally better support from the community for software. The latest processor series out now is the Kaby Lake series, using the same socket as Skylake (don't let the names confuse you too much). Generally Kaby Lake processors have numbers with a 7 in them; i.e: i5-7600K, i7-7700K etc. I would recommend going for the i5-7600K as it's a sweet spot for gamers in terms of price and performance.
3) Motherboard: There are a LOT of motherboards from different brands out there. The only think you need to take note of is the socket, which is LGA1151 if you're looking to purchase a Kaby Lake or Skylake system (both using the same socket). The chipsets are the second factor to look at. The budget chipset is H170, so motherboards from all brand for this socket will be advertised something like Gigabyte GA-H170A or something similar. Unless you have specific requirements like wanting to include an NVMe SSD, or 8 hard drives, a basic motherboard should suit your needs quite well. If you think you're going to get more serious about computer stuff, and overclocking etc, you should consider getting something from the Z170 series. As mentioned previously, form factor doesn't really matter and provided you have chosen the NZXT Phantom 410 case (mid-tower), you would be okay using either MicroATX or ATX form factors, so you don't have to worry if they will fit.
3) RAM: DDR4 (for Skylake and Kaby Lake system) Value RAM from Kingston, Corsair or any brand will work fine for general users. I would personally recommend Kingston as it's generally very reliable and has lifetime warranty. If you know that you'd like to attempt overclocking in the future, consider getting one of the Performance RAMs available as they are generally necessary to get better and morer stable overclocks.
4) HDD and SSD: I would recommend using an SSD + HDD setup. This provides a fast booting system. Using the SSD primarily for your Operating System and other software, you'll be able to use your computer comfortably with lower load times. The Hard Drive is where you store your personal files and also games. In the event that you installed something bad, and your Operating system gets corrupted, you can just reformat your computer, and your personal data will still be okay on your HDD. Good brands for SSDs are Samsung, Adata, Kingston amongst many others. I'm personally using a Samsung Evo 840 and it's been working great for nearly 4 years now. As for HDD, I like Seagate as they make great and reliable storage devices. Their prices are a few ringgit higher than Western Digital's hard drives, but I PERSONALLY wouldn't mind paying a bit extra. Western Digital is pretty good too, so either way it doesn't matter lah.
5) Graphics Card: Looking at the games you want to play, DoTA and CS:GO are more CPU intensive over GPU. This means that your CPU has more bearing on your in-game performance than on your graphics card. However, if you're talking about titles like Witcher 3, Sleeping Dogs, Watch Dog, GTA V, and newer AAA title games, these are generally more reliant on GPU. I would recommend you getting something like a GTX1060 for 1080P Gaming at high settings, and it is not too heavy on your budget, around RM1250 for the more mainstream basic editions. It should be able to give you good performance, until you decide to upgrade in the future.
6) MONITOR: With a good graphics card, there's no point if you get a mediocre monitor. Invest a bit into this part, and you won't regret. I would recommend getting a 1080P monitor with high refresh rates around 144Hz (since you want 120FPS and above). If you get a basic monitor that only has a refresh rate of 60Hz, you can't see any difference anyway. Consider getting a monitor like this or better:
http://www.lazada.com.my/acer-kg240a-amd-f...1n&ff=1&sc=ETY=7) POWER SUPPLY: Almost forgot about this last part. You need a stable power supply that can provide enough wattage for all your components. I would recommend going for an 80+ Bronze Certified 650W Power Supply AT LEAST. There are a few reliable suppliers such as Cooler Master, Corsair, Silverstone, Superflower etc. This is the most crucial component, because if you buy a cheap power supply and your house experiences a blackout or lightning strike, say Bye Bye to your PC parts. Always ensure you get a reliable power supply.
I hope I could help a bit in helping you understand what you should get. If you have anymore questions, feel free to ask.
This post has been edited by xhanetbn: May 19 2017, 08:30 PM