of course it always could be better but I've already passed my budget
i5-9600k is practically the same cpu, intel fucked up with soldered ihs and temps are high anyway
of course it won't handle i9 9900k, but I am not planning on buying i9 :)
msi z370 sli plus is above entry level and it can easily handle overclocked 8600k
hdd I've got from my old setup, 250gb ssd is enough for me as for now... I can easily buy another one in the future. There's no reason to splash money on things you don't need at the moment. That's my point of view.