First Build

Hello @Jamie84! Welcome to the Community. 

Overall that's a powerful build, but there is one thing I'd change. If you're only using this primarily for gaming, personally I'd actually switch your processor to either an i5-10600k and then take the savings from that and put it towards upgrading the video card to a 2080 super. The 10600k has a lot of overclocking headroom and with a good overclock comes very very close to the i7 and i9 parts in gaming scenarios. If you don't want to "downgrade" the CPU, I'd at least switch from the 9900k to the 10700k, since they're essentially the same processor, but you'd save a little bit with the 10700k. 

In either case you'd have to go with a Z490 board, but there are quite a few Z490 motherboards at the same price point as that Z390 Aorus ultra you had listed. 

The NH-D15 is compatible with the LGA1151 socket on the Z390 board you have listed, and the LGA1200 socket on the Z490 boards has the same mounting specifications so it will work with those as well.