Intel i7-8700K is available now, the i7-9700K and i9-9900K arrive soon, the new CPU models are likely to be considerably more expensive, but will have (for the first time in many years) a soldered thermal interface material that will help to reduce temperatures when the processor is under load.
It would appear that board manufacturers are also upgrading the new Z390 boards to have better VRM cooling for these new processors, to allow them to run under sustained load without processor throttling. Z390 boards are only now becoming available and you will find that already many Z370 boards have become unavailable in retail channels.
If you want 4K 60 fps and macOS support then you need a board with a DisplayPort 1.4 socket, MacOS does not support HDMI 2 - Apple use DispalyPort. Z390 mATX boards with this feature may be available soon - otherwise look at adding a supported GPU (no additional Nvidia drivers available at present). Some Nvidia Quadro cards may be worth considering for this purpose.
For cooling, many use Noctua NH-D14 for music production. Case options to consider, either a quiet case with maximum dampening to reduce noise or a high airflow case to keep temperatures low. A happy medium is a quiet case with high quality cooling and fans set to run at low speed to provide some airflow with minimum noise.
Nanoxia - produce some really solid (and heavy cases that are often overlooked in the mainstream.
https://www.nanoxiausa.com/collecti.../products/deep-silence-4-micro-atx-case-black
Fractal Design - well known for decent mainstream quality computer case models.
http://www.fractal-design.com/home/product/cases/define-series
BeQuiet - well known for building cases to focus on noise reduction.
https://www.bequiet.com/
To get working WIFI and Bluetooth you will probably be required to replace any on-board hardware with macOS compatible hardware. Intel wifi is common on motherboard - it has a cost advantage (perhaps also due to Intel's influence in the marketplace), but it doesn't work with macOS.
So which motherboard you get will be determined by the choice available at retail and your own requirements. As new models are coming onto the market right now, it is difficult to suggest anything until it becomes widely available or there is plenty available information from manufacturers. We are not in this position to date, but you do have some things to consider.
There is additional wifi card info in the Buyers Guide under Accessories for PCIe cards. For cards that fit directly to the board, the network section provide additional information.
https://www.tonymacx86.com/threads/guide-airport-pcie-half-mini-v2.104850/
Laptop section also has good info on wifi/BT
https://www.tonymacx86.com/threads/wi-fi-and-bluetooth-cards-for-laptops-with-mac-os-os-x.97099/
Reading some of the golden builds will also give you some more precise information for compatible wifi/BT hardware - especially builds from some of the moderators.
https://www.tonymacx86.com/forums/golden-builds.87/
There is also a music section of the forum that you might be interested in looking at:
https://www.tonymacx86.com/forums/music.21/
