You might also consider this course in Power Electronics
The questions you are asking are great questions, but require quite a bit of background that would take too long to explain. Also troubleshooting with only a multimeter will make this substantially harder if not impossible.
One of the reasons you are getting only about 50V out is because after that you'll start to get swamped with losses. You probably will need the turns ratio of a transformer to get the output you want.
Moving into transformer based designs, you can create very high voltages quite easily. Please be careful that you don't hurt yourself.