plbab,
Welcome to the gauge, and back to the hobby !. One of the "greats"of model railroading, John Allen, started with a small layout, and eventually expanded it to completely fill the basement of his home.
Scale? What are you comfortable working with? Is it too small to handle, or see? Do you have enough room? Probably, the most popular scales are HO,and N. O scale, and G scale have a good following also, but require large spaces. G scale is really nice if you like being outside, and have a yard big enough to accomodate a garden railway.
We are all going to recommend the scale we have each chosen to model in, but in the end it all comes down to what you are willing to compromise.
The smallest scale,Z, will let you have the biggest railroad possible, in a given space. The detail is not the greatest, and it is difficult to work with if your hands shake or your vision is less than superb.(like mine) As the scale gets larger, the size of the railroad gets smaller for the same given space, the detail gets better( and the reproduction of detail, if you want to build models gets more demanding), and is more visible. This is true for the trains, and the scenes they pass through. Detail that is missing in Z scale, hinted at in N, and HO, becomes required in O, and G.
It is a balance of how much detail, how much railroad, and how much effort, not me telling you that HO is the way to go, that should determine the scale you choose.
Whatever you choose, have fun with it ! If you haven't already, check out the photos posted here on the Gauge. There is a large group of excelent modelers here who have posted their work. There are great links to other sites where you may find many answers.
Finally there is this forum. You will get a variety of answers here, and, in most cases you'll find the one you're looking for.
Pete