I definitely used it as a DNS server internally and a few of the other functions. I was totally bummed to see them strip effectively all useful functionality from it. :-/
The payment industry as a whole is in the stone age.. ignoring the antiquated technology behind it all there are still a ton of industry discussions about even allowing now-legal medical marijuana dispensaries and things like that to become customers. Given that it all goes back to Visa/MC/Banks I don't expect it to change much soon.
You'll be fine with either. Just pick a camera you can afford and focus on quality glass (lenses). I personally prefer the Canon system so my recommendation would either be a T7i (DSLR) or, if you can afford the upgrade, the EOS R (Mirrorless and my current primary).
Biggest con these days on mirrorless is they tend to run through a battery charge about twice as fast as a DSLR equivalent.
For materials.. as much as I've not been fond of youtube in the past for whatever reason I find it extremely valuable today. Peter McKinnon is pretty great or if you want to start with landscapes maybe check out Thomas Heaton.