The ASRock H170m Pro4 doesn't have stellar reviews at Newegg. Did you read their user reviews, starting from the negative, and working your way up? Even the 5 star reviews are under 40%, and adding up the 4 & 5 star reviews you come up with 53%, so figure that you have a 50/50 chance of getting it working correctly right out of the box. (You have a 50/50 chances of having problems, too.) Have the latest BIOS updates fixed most of the old problems? idk. Just figure that you may experience SSD boot problems, just like any other mobo, but perhaps with a greater chance than other, better, mobos. If you desire to overclock the CPU - forget all about overclocking. If you want to overclock a slower processor to be as fast as the fastest stock processor, save yourself a lot of grief and just buy the faster processor.
What's a "cheap" HDD?, when you're also installing a cheap ($) SSD? Did you read the Newegg reviews on that SSD and see what problems other users have had, or are having? Lots of people have problems booting from SSDs, and once you format it you may need other tools (Linux and even Windows) to undo it (say, from changing from UEFI boot to UEFI-Legacy boot). If you will be dual booting it with Windows it is almost a certainty that you will have problems.
Can any suggestion guide be trusted completely? Probably not. But chances are that it is an all-around/average guide for most users. For example, I would never install a 32MB cached drive when I can install 64MB cached drives; I would never install 5400RPM drives when I can install 7200RPM drives, etc. Lots of times it's a matter of preferences, what the user knows will work better or what the user hopes will work better. You pays your money, you take your chances. If it's guarantees you want then buy a Mac from the Apple store.
Your success rate may be tied to how technically savvy you are. And if you are that technically savvy you should already have an idea of what will and may not work. You say,
Will it work as a Hackintosh? (given that all the components are featured in the buyer's list). I cannot find a Hackintosh build with the motherboard I plan to use, but it is the cheapest one on the list
If it's on the list then it is known to work. Or at least it is known to have worked. That's not to say that you won't have problems. It may have worked with Mavericks, it may have worked with Yosemite, it may even now work with El Capitan. That doesn't mean that it will work with Sierra. Or the OSX after that, or the OSX version after that. Just look at Apple's own record - Power PC CPUs were dropped, 32bit Intel procs were dropped, older MacPro 64bit Xeons were dropped, Sierra is dropping any machine older than 2009.
It's interesting that you can afford a GTX970 and yet you are willing to mate it with a slower processor, with less than the max memory, with slower SSDs and "cheap" HDDs. I'm not saying that you are wrong, mind you, just that it could be a better balanced system. Will you run into any issues? Probably. And your chances are as good as anybody else. Heck, I had problems and I've been a computer tech for over 40 years. But, no, I didn't have any hardware problems.
If you want to maximize your chances of a successful build you can start with the PSU, buy the fastest processor (and that is on the MAC ID list), install the max mem that the mobo can hold, stick with 64MB cached 7200RPM HDDs, use the stock Intel CPU fan, make sure that the computer case provides adequate air flow. Cheap mobos are easy enough to change out... (And at over $80 that isn't exactly a cheap mobo.) But, did you see where one LG 25UM65 reviewer on Amazon said "This is not mac compatible i tired my other split screen also from lg( works great with windows 7), it worked just as well with my mac book pro, it just says it in the description for mac users to buy this."? Is he right? Why did you choose such a wide screen? Have you seen what text looks like on such a screen?, what a video looks like on such a screen?, what a game looks like on such a screen? What is the res on that screen?
