Agree with others, Vaultwarden is probably your best bet. I’ve found the default app to be a little flaky, but ended up using Keyguard, which I’ve found really good.

I used to use Keypass+Syncthing, but found sync conflicts too often (due to Syncthing support for Android), hence the switch.

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?