I can’t turn it off because none of the lightbulbs in the house would turn on anymore

If you have Hue bulbs, you can buy little radios that attach to your light switch (or replacement light switches) that will still operate your lights when the server is down or the network is unavailable. It’s a worthwhile upgrade.

Is there a reason to avoid Nvidia cards on Proxmox still?

First things first: Synology as a beginner NAS is perfect! It’s what I recommend to everyone that is getting started out. So good move there.

I think you should get a four-bay NAS. You don’t have to put four drives in it; you can put two drives in it and have an upgrade path for later. Plus the drives are far easier to install and remove. The processor will also be better in a four-bay NAS, which will give you more options if you want to play around with a docker container or run a VM.

To answer your questions:

1. If the NAS you choose has a USB port on it, you will be able to connect things like external hard drives, thumb drives, etc. NASes with USB3 connectors support USB 3 drives. Just be sure to use a file system that is not proprietary. So NTFS is out, but exFat is fine.
2. I have connected to volumes on the NAS and have connected the NAS to other volumes without issues. It will work fine.
3. I had two NASes sitting right next to my head in my office at ear level — probably the worst case scenario for noise. I barely noticed them. I could hear them crunching away during backups, but it wasn’t bad. I never heard a fan running — just the internal drives making their read/write noises.
4. The drives fail before the NASes do. Synology had some issues with bult-in power supplies going bad after a few years. Their modern NASes now have plugs with a power brick on the cable, which I assume was in response to this issue. It’s a lot less expensive to replace a power cable than a whole NAS! But beyond that one issue (which affected one NAS of mine), the NASes I’ve been using have lasted for … oh, 8 years now.
5. There are many choices for syncing data with your synology NAS. They provide Synology Drive, which gives you a local drop-box-like folder syncing option. They support rsync, and they provide HyperBackup, which is a block-level backup utility. You can choose a Synology shared drive as the destination for a Time Machine backup on a Mac. (I assume you can do this with Windows’ backup solution, but I’ve never personally used it.)

Porkbun is sort of the darling of the self hosting community. I settled on them after doing a huge comparison of prices and features of all the different registrars available to me. Porkbun was by far the best.