Hello Captains,

So I finally felt like I am ready to jump from regional smaller aircrafts to airliner and after long searches and doubts, have decided to choose Captain Sim 737. Have even already made few smooth flights and need to say I do not regret of my choice 
I am falling in love with this plane faster then I can study manuals for it.
Lucky for me, I don't have any issues with it, everything works just fine (fingers crossed). So there's only one thing I don't like about it and it's GPS navigation. But it is what it is. As I have seen in other topics here, there are some third party FMS products for it, but somebody also said that this plane was not designed to fly by FMS. How was it flying than? VOR to VOR?
So my question is, how do you guys create realistic flight plan to fly this wonderful plane? I do have a Navigraph subscription and it brings even more satisfaction to flying, but to fly SID's and STAR's you need to have a decent FMS. So was this plane always vectored on approaches?
I've tried to upload a flight plan in P3D flight planer which I created with SimBrief, but it looks like it is changing automatically and some points are different, so SimBrief is also useless in here.
In other words, what is the most realistic way of creating flight plans and flying this plane as it was flown in that era of flying?