Current planned use cases are Pi Hole, Bitwarden (password manager) server, probably general network storage and torrenting, whatever other "homelab" things I think of later (which is why the specs probably seem a bit overkill)
Lenovo ThinkCentre mini desktop, eBay refurbished, $184 before tax
8GB RAM, 500GB SSD
Intel Core i5 6th Gen. (they don't specify but I'm assuming it's a 6000 series, which was released in 2016)
Direct link to the listing: https://www.ebay.com/itm/293526962748
I'm rethinking the storage and might just go for 1TB HDD, which brings the price down to $151. Not just for lower price/more storage, but because considering all this is used, I don't know how many cycles the SSD has on it. Do you think this would be a good or bad idea?
New HDD or used?
HDDs are a lot more sensitive to travel/shaking, I wouldn't buy one that isn't brand new from a legitimate store. Or if you're running a used one, then run two mirrored so you're not boned when it dies.
Used SSDs you can check the wear level after it comes to know how much you should trust it. HDDs are more of a toss-up.
I think it's still good to go with the HDD instead. You can always later get M.2 SSD with a USB enclosure if you run "busier" databases that will benefit from faster speeds. They're small enough to dangle from USB ports.
When you go refurbished it's always luck when it comes to any type of storage. My server's root fs runs on an SSD that's like 10 years old, yet I bought second hand hard drives that are 4 years old and they were broken beyond repair.
Make sure to backup your stuff regardless.