Railway Modelling is a great hobby. It involves so many disciplines. You can put together all the components to build a model railway but it can take something special to create a model that looks right.
I spent a great deal of time planning the perfect model railway and was sniffy at other people’s attempts. But the important thing to realise is that they were running trains, and I never did.
And size doesn’t matter. One of my favourite models on the exhibition circuit is only two feet wide. But it is a beautiful model. The most important action is to build something, even a non working diorama.
On the subject of size, be careful of the layout that grows in size because of the law of squares. A model that doubles in size will require four times the work, and four times the cost. Trebling in size increases the work nine times. There is nothing wrong with planning in a possibility of expansion at a later stage. And a layout is never actually finished.
But the best advice I can give is that it is your layout. You build it the way you want, run what you like, the way you want. Have fun.
You may or may not agree. And like any critic pontificating from the sidelines, I don’t follow my own advice.