Yeah, it’s a good enough CPU for now. The 3600 is €25 less than the 3600X, either one is fine.
My bad, I misread that as 16GB not 2x16GB. Teamgroup, a no-name brand has a good 3600 MHz option at €106.79, should work but otherwise a G.Skill or Kingston 3200 MHz stick kit is available at roughly the same price. 3600 with good brand is another 20-25 euro.
To be honest, at the suggested price point you won’t be getting much better performance for now. You want to go RTX-class, you will need to plunk down at least €500.
This could be very easily achieved with partitions - But you are right in that it is a lot less hassle to work with two separate drives. Unfortunately Windows and it’s applications can easily grow to 100s of gigs even without games - with games, it’ll be even worse. I would in that case invest in a 1TB NVMe drive for now and look at getting a 2TB or even 4TB SSD later.
It’ll just be so much easier with a 4k editing rig to go full SATA, than having to start every editing session with 30 minutes of copying clips over from the mechanical drive. Also, have a look at solutions for hot swapable harddrives, really helps with getting footage from cameras if your camera is new enough to support that ofc. 
