"TrinityCore is an MMORPG framework"

Not sure where to post this.

I’m letting it compile right now and I see lots of handlers and then scripts there’s a core of objects and network communication and handlers and there’s scripts specific to WoW.
The description says it’s a MMORPG framework.
What exactly can be modified? I mean it’s very close to WoW, right?
I saw a thread about missing .proto files. Does WoW communicate via protocol buffers?

Where would I start if I wanted a clean server that is able to provide authentication?
Can I design my own “classes”?
What would I use to write scripts?
Can I for instance say “every new player spawns in 1 region”

What about stability and security as in offbyone and similar faults?
Do you have a pentesting team? Did you run any fuzzers against it?