You don’t have to do anything else with the domain, it’ll work fine for email only.

You could add it to Proton, take your time to migrate all your accounts, then dip. Or you could just go straight to a new provider with the domain, and take your time transitioning accounts to the custom domain over time that way. Assuming Proton’s free offering is sufficient, you can always keep it around and set up forwarding to your custom domain.

Regarding domain name setup itself, Proton should provide steps for how to do it correctly, but I found them to be a bit fiddly (might have improved, this was a few years ago) - when I moved to Zoho I found it really easier. If you’re using Cloudflare for the domain registration, Zoho can basically do it all automatically (click a few links link and accept the proposed changes).

Just don’t be this guy…

If you’re looking to shake up your email provider in the wake of this, I highly recommend getting a custom domain name, whatever provider you choose. Cloudflare sells domains at cost. Get a not-embarrasing .com of your own, and then you can move email providers in future without losing continuity. Proton allows exporting .eml files, which you can then import into your next provider. Or just keep in cold storage and declare email bankruptcy. Once you have a custom domain, you can use unique emails for all your services by setting up a catchall address. This will at least impede credential stuffing attacks, and let you know who sold/leaked your address if you do get spam.

I personally left Proton a month or so ago after the last bit of drama, in part out of principle, but also because their offering is just really expensive for my use case: I just want email, on a budget, with reasonable privacy. Plus I was tired of not having IMAP support and being locked into their clients. Moved to a Zoho business account (for now) and have been happy for the $12/yr. I already had a domain name, but they typically run <$20/year too.

Anything USB connected more likely to be flaky, but a good enterprise disk shelf and a HBA card would be rock solid (just noisy…)

Unfortunately my solution when I did a big data migration was to buy more (cheap) storage lol. Ultimately it was a cost vs. time/stress tradeoff.

Physical space is actually a huge issue

Ah then I’d recommend keep the existing machine as the server (it sounds like it’s serving you well hardware wise), and get a SFF machine for regular desktop use, be that a new build or a used office machine. The trick will be in migrating the server to Linux, and without endangering your data in the process.

Examples of some of the deals I’ve personally gotten (ymmv, some were auctions):

• 5 x 3.84TB SAS SSDs
  • $521.54 total (stunning deal, I got lucky)
  • $104.31/drive
  • $27.16/TB
• 5 x 960GB SAS SSDs
  • $165.17 total
  • $33.03/drive
  • $34.41/TB
• 7 x 12TB Toshiba SAS HDDs
  • $427.31 total
  • $61.04/drive
  • $5.09/TB
• 2 x 8TB Seagate SAS HDDs
  • $49.99 total
  • $25/drive
  • $3.13/TB
• 2 x KTN-STL3 JBODs each including 15x3TB SAS HDDs
  • $532.73 total
  • $266.37/shelf
  • $17.76/drive bay+drive
  • $5.92/TB not including value of JBODs (~$150/each without drives)

In short, I’d recommend option B/C, where you buy used enterprise grade equipment, learn to run Linux, and build out that way. I can’t overstate just how good a deal can be had on eBay, even from reputable sellers. This goes for everything, from the computer itself, to disk shelves, to HDDs and SSDs. Plus you’re reducing on e-waste! Used HDDs are a great deal if you buy enough to run redundancy (RAID 6 or equivalent), because the seller will often include a warranty (up to 5 years!). I’ve only had a handful of drive failures and 0 issues with warranty refund/exchanges.

You’re running roughly the same services as I do (though a bit more storage), so if it means anything, I’ve ended up using the following (all purchased used)

Broadly, I find the following with my setup:

• Pros
  • Easily expandable storage using a HBA
  • High reliability (ECC memory, server grade equipment)
  • Used equipment is cheap
• Cons
  • Running mostly older-gen hardware, not cutting edge performance
  • Bulky, noisy cooling, less power efficient

A few things that might help narrow options down:

• What’s your budget?
• Do you expect to host more stuff in the future? Do you need more RAM/CPU performance?
• How much physical space do you have? Do you have a place where could store equipment if it were noisier?
• How expensive is your electricity? Is efficiency important?
• How much of your 100TB is full?