I agree with the 2 previous posts. You have to finish a couple then release them as freeware, you might even have to do quite a few before making a payware asset. Also, if you get frustrated with a project, perservere and try to figure the issue out. Or even better, ask for help, I am fairly sure that there are plenty of excellent content creators who would not mind giving you some useful advice to help you complete your projects.
A suggestion that myself and most other content creators would give you would be to start with something simple, texture it, maybe do an animation and export it to trainz so that you get some experience going through that process. You may also even want to figure out how to turn that simple mesh into a train car, basically you would be adding the necessary attachment points in order for it to function as a train car.
My attitude =/= The Back Shop's Attitude
Models, Scripts and dependencies.