From personal experience, the radiator does fit in, but it is almost glued to the plastic. (Unfortunately, I can't say in advance whether you need such a good cooler. But it's better to have a little too much cooling capacity than too little. You can use such things for years. If you want to upgrade your rig later, it's worth getting a better cooler now). I can't recommend a Pure Rock Slim, because the cooling performance is not much different from a Ryzen 5 stock cooler Wraith Stealth. (On my Ryzen 5 3600, so it's in the same performance class as your i5-10400F) I recommend the Noctua NH-D15 (16.50cm) as the cooler, because the price difference between the two coolers is only 8 Fr. and Noctua NH-D15 cools 5 Dgree better on average. And it comes with a very good thermal paste, which you no longer have to buy yourself.

The GPU is probably too fast for the CPU if you're gaming in 1080p. If you're gaming in 1440p, it's a balanced system.

A few more tips from me about this case. It's made of very thin metal, I accidentally bent the GPU bezel with very little force. And since the side window is plastic, it's really hard to clean compared to a glass window. For this, my recommendation:
-If you need a side window: Fractal Meshify C TG
-If not: Fractal Meshify C
If they are too big for you, you can also buy the mini version of this one. Then the Dimension ones here are somewhat the same size as these cases. And yes, a matx motherboard fits easily into an ATX case. (Mini ITX too)

Finally, the last one: IMPORTANT: If you don't need the PC urgently, WAIT! The new GPU from AMD and Nvidia will be released soon. They offer much more performance for the same price. (maybe a bit higher price, but it's worth to wait and see) Also the new CPU from AMD is coming out, but an i5-10400F should be enough for the next 3-5 years, if you only want to gamble.

If you have any further questions, please don't hesitate to contact me.

Best regards

The cooler is too high, apart from that a smaller model is perfectly adequate, you can't overclock the CPU anyway. The rest of the components all fit together.

Personally, I would go with a Ryzen, better price/performance.

The Dark Rock Pro 4 is unfortunately too big for the case, but I think you can also live well with a be quite! Pure Rock Slim (12.48cm), as you cannot overclock your CPU. The length of the graphics card fits in the case and works well with the CPU. You could also use a Gigabyte Radeon RX 5700 XT Gaming OC (8GB) and pay less for similar performance, but depending on what games you want to play, these are optimised for Nvidia or AMD. If you go with the RX 5700 XT, you can still buy a Kingston A400 (480GB, 2.5") with the money you save and have doubled your memory capacity. I hope I was able to help you and if you have any questions, feel free to get back to me.