There are several things to consider here, such as whether you are going to model a freelance situation or a prototypical one. If prototypical which company and in what era, the steam age, modern times or the meeting point of the two? What kind of running do you want to do when the rails are down, continuous, there and back or a mix of the two? The kind of running you decide on will be the lynch pin of the whole model because your basic track design will have to reflect this choice.
You may say that you don't want to be bothered with any of this, you just want to see some trains running. A quick answer would be, don't we all. However that's not very helpful, so I would only say that in my experience of other modellers, who have said the same thing, they have quickly changed their minds as their model began to take shape and they could see the possibilities. Their ever growing skills are then being applied to a model that means something, that has a purpose.
A decision taken now, on the choices shown below, could well save you a lot of money on kit that is inappropriate but in the long run would make no difference if by some chance you stayed with just wanting to see your trains go round and round.
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