Thanks for this very detailed reply.
1. I think I'm going for the 3700X to future-proof the system.
2. I'll check the prices of RAM (16GB vs 32GB) and see what I can do.
3. I already have a Samsung 970 EVO 500GB nVME m.2 drive so that's going to be the boot drive. I totally agree with nVME drives being a must for ITX builds, just to make everything neater and airflow not too "choked". I'm thinking no mechanical HDD's because we already have a NAS at home but I can always add a 3.5" HDD to the system if really needed.
4. Would a GPU be super necessary/useful for her use case? Would she be golden if she just ops for a 2060 Super? Or would it be better to just invest a little bit more and opt for the 2070 Super? When will the non-blower style RX5700 XT be released anyway? I'd also want to go with a mini card.
5. I'm a custom watercooling guy (pic of build) so I'm not afraid of getting my feet wet, so to speak. So an AIO for the CPU in my Sister's build is an absolute must for me.
6. For the mobo's, I have no idea which one to choose. I read that it's only Gigabyte that released an X570 so far. I'm an ASUS mobo guy but my NAS has an ASRock board. Any particular mobo recommendation in mind?