Spock said in Amok Time, "Stan, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical but often true."
Spock was talking about his fiancé, but I think it works for trains as well.
For the longest time, all I could afford was the catalog. There are so many ways to enjoy the hobby, I have gotten a lot of enjoyment from MPC era stuff.
I started with a 4by8 table then added a second. I only screwed a few of the track pieces down here and there, no ballast. That way when I expanded my layout, it was easy to configure and reconfigure the track plan.
I have expanded my layout twice, I did find that I tended to like to just run my trains, not doing much switching, so I probably did not need as many switches that I have on the layout. So, knowing what and how you will be running trains may help save some money.
Developing a track plan can be fun, a simple approach may be the best, especially for the first layout.
Building the layout so that it can easily be broken down and transported makes a lot of sense.
My layout has one line (out of three) than has 54 inch curves, the other two lines are 36 inch. So, by design I have limited my purchases to smaller sized engines.
Scenery can be challenging, for the hi-rail look, I highly recommend the Dennis Brennan "Realistic Modeling for Toy Trains, a high rail guide". He covers everything from benchwork, wiring, scenery, etc. the one difference I make with ballast, I only ballast outside the rails, and nothing beween the rails. Most people don't notice.
What I have not done well is to sell or give away, equipment I don't need, I started an eBay store to sell baseball cards, so at some point will pivot to selling trains. Obviously the OGR Forum is worth a try as well.