Hi and welcome!
I guess first things first: scale. As you're posting on the N forum (I couldn't see you on HO), I assume you've decided on this scale (very wise!)
The next decision has to be where in your house/apartment you want the railway, and how much space in this area you can use for the railway. For example, if using a basement - can you have all that space? If a spare bedroom, does anyone else need part of that room? If running through the house (to bring cups of tea etc), will anyone else in the house object to that idea!? (By the way, I'm not sure N scale trains could actually carry anything but very small cups ...
)
Once you've got the location and size sorted, you want to decide on era and railroad. Are you going to be multi-era? Are you going to run a specific railroad, several ones from a similar region, your own fictitious railroad, or just mix it all up anyhow?
Then you need to decide on track type: in N we have two main codes (i.e. height of rail): code 80 (which is too big prototypically but older and more recent models will run on it), and Code 55 (which is closer to prototypical scale, but some older models will need adapting because their wheel flanges are too deep).
At this point you can think about track plans, maybe consulting books and websites that have a range of track plans.
Hope this helps - keep us updated!:thumb:
