You never said what kind of frame you had other than it was a custom. What kind of geometry (road, hybrid, comfort/cruiser, etc..) are we talking about? I will assume it's a road bike.....having said that, if you like the way the frame feels and like the custom fit, then just upgrade your components. I would start with a good set of tubeless ready wheels. If you like the way the steel frame feels now, it will feel even better on tubeless tires. Next I would upgrade the drivetrain with your group of choice.