I have had to create the joiner piece of the track separately in order for them to match up to each other perfectly. With this, I can them import it into any other scene file and carry on modelling from there. I find importing a really useful thing, it allows me to check my models against others to see if I'm on the right tracks. Another thing I have found to do is create layers, just like in Photoshop you are then able to make specific things visible or have them turned off. This allows you to concentrate on one particular area without having too much on screen.
So far I've had a lot of problems, not necessarily with the actual model itself but more of the fact that the train can't line up on the tracks properly without cutting into them. The above image (top track) shows how much wider the it needs to be when going round a corner. The original tracks look more attractive and are more like the real thing, however it is just not practical, unless of course I had a massive curve but then I think it will be too big. If I decide to have a curve I will need to go back and re-model the other tracks - it shouldn't take too long now that I know what I'm doing.