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