The Quest for a NAS: Rackmate T1 Question

I am looking to complete my all-in-one network/lab rack build with the addition of a NAS and would like some guidance. I've laid out my parameters below. What is a good solution for my needs??

## The goals:
1. Backup two PCs and YouTube video production *(live streams mostly)*
2. Personal cloud service *(calendar, photos, forms, notes, etc.)*
3. Home Assistant VM
4. Plex/Jellyfin media server
5. Docker *(educational, see technical ability)*
6. Powerful enough to manage all of the above while staying *(relatively)* power-efficient
7. 4-bay HDD was the original template *(DS923+)* but I am eager to hear other suggestions

## The technical ability:
* I have "beginner+" technical ability. For example, I am familiar-ish with git and the command line, but am not often capable of solving problems I get myself into. Following detailed guides for setup is the space I am able to exist in *(for now)*

## The budget:
* My budget is flexible for the right system, but I am okay stretching it to ~$2k USD
* This budget includes 4x HDDs around the 12-16TB size

## The build space:
* 4U of available space in the 10" Rackmate/GeeekPi T1 rack
* A compact 4-bay HDD NAS should reasonably fit within this space - the TerraMaster and Synology 4-bay lines are within spec for it
* This was designed with the Synology DS923+ in mind, but I am hesitant to sign up for a system so outdated when an upgrade might reasonably be expected to arrive within 1-2 years