Good luck gb! All the best. I had same problem when I switched to UDK from Darkplaces engine. I have developed a quite good knowledge of Unity and UDK platform. UE4 is too much young for me now, I'll let it "mature" a little more!
If you need some input just pm me. I anyway reccomend you Unity because its development learning curve is a breeze and I suggest you some extensions that could fit to your needs: PlayMaker, UFPS and ORK Framework (since, if I understood correctly, SJ will have a RPG soul). With a bunch of euros you can have a preconfigured game framework that just needs to be customized!