Advice for reusing an old system as a NAS/Homelab?

[KoalaKing]

Budget (including currency): I don't really have a particular budget in mind, I'm just asking for some advice, but if one is needed, I would say $500 USD to start.

 

Country: United States

 

Games, programs or workloads that it will be used for: My goal is to run the following applications on this system:

• NAS Software to backup the systems on my network, as well as for general file storage, to clean out computer drives (probably Unraid). The systems that need backups are:
  • a 1 TB Laptop
  • a gaming system with a 1 TB boot drive, 1 TB Game Library drive, 1TB Internal Backup Drive, and 1 TB secondary OS (secondary OS is less important to backup)
  • a gaming system with a 1 TB boot drive, 2 TB Storage drive for video editing, and a 500 GB spare storage drive that's not used very often
• Ente - Photo backup from my phone (so I can ditch iCloud)
• Minecraft Server - Something small for a few friends
• Plex/Jellyfin

I'd also just like to maintain some room to tinker with other things in the future, like tinkering with Home Assistant, other game servers, etc.

 

Other details (existing parts lists, whether any peripherals are needed, what you're upgrading from, when you're going to buy, what resolution and refresh rate you want to play at, etc): 

Currently I have an older system in storage with:

• MSI B250M Gaming Pro Motherboard
• 7th Gen i3 (I don't remember the exact CPU, I think the i3-7100)
• 32 GB DDR4 2400 Crucial Ballistix ram,
• Gigabyte Nvidia GeForce GTX 1660 Gaming OC 6GB GDDR6
• EVGA 450 BT PSU (I'll probably want to upgrade this at some point, even just for efficiency)
• Case with room for up to 4 3.5" HDDs (I could get up to 4 more by adapting 5.25" bays to 3.5" drive bays)

I also have an Intel Optane M.2 drive that I bought a while ago to use as a cache drive, but I haven't had the chance to use it yet.

 

With these details, I just have a few questions:

1. Is the hardware I have powerful enough to run all the kinds of loads I want to run, or would I need to upgrade?
   1. If I need to upgrade, would I be better off just going with a pre-built solution?
2. How much storage would I realistically need if I want to be able to backup all the systems listed and still have like 4TB of usable storage space?
   1. I'm expecting I'd only use 1 parity drive and have email notifications setup to let me know if a drive has failed. With this in mind, I'm expecting I'd need around 12 TB of usable drive space, and I'm imagining 4 4 TB drives (1 Parity, 3 storage) would probably work, is that correct?
3. Is there anything else I should keep in mind for when I go to pick drives or other upgrade parts?
   1. E.g. Do I really need "NAS" designated drives for a home setup like this, or will standard drives be fine?
4. Any other advice in general regarding NAS/Homelab setups?

I'm not planning to build anything immediately, I'm just trying to get a sense of what I need to be saving/looking out for so I can build something great sometime down the road.