The characters in the ST and their arcs are original, that’s good enough for me.
Yes, they are and, IMHO they are the best part of the ST thus far.
The new characters (Finn/Rey/Kylo) were created by George in his story treatment for the ST.
The single moment that put RJ in the position he was in when dealing with Luke in the TLJ is what happens in Starkiller base in TFA. JJ didn’t have Luke come to Han and Leia’s rescue. By having him allow Han to be killed, RJ had to have Luke be “broken” to explain it away.
You can agree or disagree with Luke’s character portrayal in TLJ. But it isn’t Rian’s fault. JJ left him nowhere to go.