For future reference, you might find it helpful to read "man defaults" and "man PlistBuddy". And its binary is at /usr/libexec/PlistBuddy.
I can't say I blame you, though. Figuring out what all these tools did and what they were for required a fair amount of reading and experimenting on my end.
Binary plists have been around for ages, in fact they come from NeXT. But most stuff on OSX will still happily interpret XML (and now JSON) based plists just fine if need be. For all your conversion needs there's plutil.
As I said: not my area of expertise. Though the docs I was reading were suggesting that the change from file to binary had occurred after OSX was introduced.
I've been happily using macOS server at home for a few months. It's not a production-ready deployment, but I haven't had any complaints.
Aside from that, using it on my personal laptops has worked surprisingly well. Once I familiarized myself with the CLI tools, I haven't had any issues.