Can't sleep, feel like poo, so I'll try to throw some anecdotal info together. This is broad strokes, please excuse generalisations. Hopefully you find something useful.
Motherboards
I believe the reason people are suggesting the Gigabyte boards is better build quality, and more capable VRMs, but I'm out of the game somewhat.
My advice is think about what you want; connectivity, RGB, accessories, price, SSD support, audio, bios etc and pick what best suits what you want, for what you're willing to pay.
Brand loyalty doesn't earn you any favours.
Fan Control
I recommends using a dedicated fan controller. Hackintosh compatibility I have no experience with, so bear that in mind.
If you want simplicity, iCUE and a Commander Pro is a good bet. The ecosystem is well put together, but their support isn't great and they'll happily leave customers in the dust when they move onto a new product line. There may be issues with Hackintosh, I believe iCUE needs to run for the controllers to operate properly.
AquaComputer make an absolutely awesome range of controllers and components. The software is incredibly powerful, the support is amazing, the possibilities are limitless. Price of entry is higher, learning curve is steeper. I don't believe they make Mac software, but their controllers can be set up in a windows environment, saved to the device, and disconnected from USB. They don't need software to operate.
Water Blocks
Most blocks perform the same. It's about aesthetics, features, and some slight variation on mounting method. I like EKWB, I do not like the Corsair line up at all. It's mostly aesthetic, and some things I've not liked the look of during teardowns. Corsair kit is fine, it's very accessible, and very rainbow chunder, if that's your bag.
Pump
Get a D5 unless space is an issue. The DDC is a fantastic little pump with better head pressure, but it's noisier, hotter and has lower throughput. There are others, I'm not well informed enough to comment on them. Use a pump top. I prefer my pump to be seperate from the Res, many opt for an all in one unit.
Radiators & Fans
The most important components, these will dictate the type of build you have. Your case will dictate what size, thickness and port configuration available / needed, and this in turn will affect the fans you choose.
Slim rads will perform worse, unless they're more restrictive and have higher FPI. Higher FPI fans require more static pressure, which means higher static pressure fans, usually running at higher volumes. Restrictive radiators will require a higher pump speed, or a higher head pressure.
If you want silence, you want more rad space, lower FPI, and quiet fans.
If you want performance, you want more rad space, higher FPI, and higher static pressure / faster fans.
If space is an issue, you want slimmer radiators and fans that suit them.
I recommend HardwareLabs Black Ice GTX / GTS. They're great.
Fans Cont.
For fans I've gotten on well with Corsair ML120 Pros (not a fan of the 140mm, scuse pun) and Noiseblocker Eloop. Noctua, EK Vardar, BeQuiet! etc are all good choices. There's loads of good fans out there, take your pick.
Fluid
I do not recommend coloured fluid. Yes it's all the rage, yes it looks cool, but clear is best imo. I use Mayhem's XT1 Nuke clear concentrate, added to distilled water. I recommend you choose this over de-ionised, if it's available. Double check there are no compatibility issues with your tubing and fluid of choice; Mayhem's has good charts.
Clear doesnt discolour acrylic blocks, reservoirs and tubing, it doesn't seperate, it's less inclined to gunk, and imo is the lowest maintenance. Others will undoubtedly say I'm wrong, make your own decision.
Tubing
I don't like hard-line. I'm a simple man. Flexible tubing is easier to build, easier to modify, makes it easier to tinker in your system, it's cheap, and there's lots of colour options.
The reason most people go for hard line is the aesthetic. I don't like the look except in ultra high-end custom builds. I use EKWB ZMT tubing, I love it.
Fittings
There can be some variation between fittings and sizing. Make sure yours fit. Fittings are one of those things that can really add to the cost of the build quickly. And remember; no matter how many extras you buy, no matter how many adapters you add to that basket, you'll always need to order more
Configuration & Tips
1) New rads will need to be cleaned thoroughly. I recommend Mayhem's Blitz. This is an important step.
2) A drain port is really, really useful. Lowest point in the system, or designed so that reorienting the case makes it so.
3) A fill port isnt necessary, but it's nice. Just don't design your loop so that the reservoir is a pain to fill.
4) A bigger reservoir is better. Less opportunity for air recirculation, easier to fill the loop. When designing the layout, I prefer for the return to feed into the bottom, as air isn't pushed towards the pump intake. A deflector plate or inlet tube is needed for this config. It goes without saying that the reservoir should directly feed your pump.
5) PWM provides much finer control. I recommend you use PWM fans. A PWM pump has pros and cons. No control until the system is up and running, and many people don't adjust pump speed after initial setup.
6) Perform a leak test with a shorted ATX connector, you can buy adapters for a couple of quid, or make one yourself. I like to leak test with a separate PSU outside of the system. Whack paper towel down etc, you'll see it in every watercooling guide.
7) Avoid right angles where a straight line will work.
8) Pump failure and detection should be accounted for. The easiest way is for the RPM lead of the pump to be connected to the CPU header on your mobo, and an alert / shutdown configured in the BIOS. iCUE has good functionality in this regard, AquaComputer have a physical Cape that connects directly to your power switch, and you can configure various parameters to trigger a shut down.
9) Controlling fan speed based on water temperature will make fan curves smooth, and avoid sudden ramp ups.
10) Flow sensing can help you spot a problem early. A recent thread demonstrates this; someone found s gunky lump in their CPU block before they had issues.
11) External / additional temp sensors are very nice, you can plot some cool data, and monitor some geely stuff. A single water temperature sensor will give you all the information you need to get up and running.
12) Don't be obsessed with matching equipment. Get the best product for the best price.
That's it. Hopefully there's a nugget or two in there for you. I'm going to try and sleep. Good luck with the build mate. Look forward to the project log