Would a rendering machine really use up a lot of RAM? My original plan was to go with a 2x8GB 3600MHz CAS16 as I've read that this is the sweet spot for Ryzen 3000 CPU's but I'm not sure when it comes to 32GB kits.
Do you think it's best to invest on a 3700X instead of the 3600?
For big scenes yes you need more ram. But it doesn't sound like you're a pro so stick with 16gb.
Depends on how fast you need your scenes to be rendered. 8 cores should be 30% faster than 6. A 6 minute scene into a 4 isn't that fast, but 30 to 20 minutes may prove useful for the life of the cpu.