Love to give opinions ....I have no skin in the game.
Some thoughts:
Love ITX builds, and that looks like a good case.
I5-7500 comes with a perfectly adequate cooler.
Spend the cooler budget elsewhere.
RX580 may need more than 450w:
http://www.realhardtechx.com/index_archivos/Page362.htm
Also, because of the resurgence of cryptomining, the RX5--- cards seem to get overpriced.
GTX1060 is in the same performance class and takes less power. 450w is fine.
Look for one with blower cooler type cooling.
Such coolers get hot air out of your case directly.
Important in a small case.
I will never again build without a ssd for the "C" drive. It makes everything you do much quicker.
120gb is minimum, it will hold the os and a handful of games.
But, many things default to the "C" drive.
When a SSD nears full, it will lose performance and endurance.
240gb is the recommended minimum.
If you can go 240gb, or 500gb you may never need a hard drive.
You can defer on the hard drive unless you need to store large files such as video's.
It is easy to add a hard drive later.
Samsung EVO is a good choice for performance and reliability.
Most of the time, 8gb of ram is fine.
Still, though, I would try to do a 2 x 8gb kit.
The extra cost os not much . 2400 speed is fine.