Cores and Threads count are really important now, so a i5 9600K is really barely there in terms of performance. If the software you are using don't use many threads it will be great, but if the software is capable of using as many threads as it have available then you will be facing longer render times (just as LORDPrometheus said).
As LORDPrometheus wrote, Core i7 9700K with 8 cores will be a bit better choice, but yeah the Core i9 9900K will be the real long term answer on Intels platform.
Now on AMD you could easily spend less money going with something like a Ryzen 5 3600 (6 cores / 12 treads) + a really good (if not the best) tower air cooler Noctuas, like
https://noctua.at/en/products/cpu-cooler-retail/nh-u12s-se-am4 or
https://noctua.at/en/products/cpu-cooler-retail/nh-u12s-chromax-black; or a Ryzen 7 3700X (8 cores / 16 threads) + same cooler or bigger (Noctua have better 14mm fan cooler options too).
Theres also the Ryzen 9 3900X option 12 cores / 24 threads but for your line of work seems overkilling and is really hard to find one.
Also don't forget to factor RAM and storage, a good amount of RAM (atleast 16 GB dual channel kit of good speed/timmings) will reduce the chances for the system to start swaping info to the "slow" hard drive because the RAM is not enough.
Also a 2 hard drive setup is always the way to go, 1 SSD, 240 GB should be more than enough for Windows + Programs, + 1 big HDD/SSD for the big image and video files. (You don't reslly need nvme speed but it wont hurt, a good sata SSD will be enough). SATA SSD also come in m2 format and can be inserted to the motherboard without cables.
Cheers