4. Track and Track plan
There is a wide range of commercially available track today, and this is probably the best approach for the novice. When you have gained some experience, you might want to consider building your own.
Commercial track is available in short pieces of set lengths and curvature -- called sectional track -- or in longer sections that you can bend to suit your own needs. Sectional track is good for some applications, but it can be very limiting. If your railway is not to be permanent, sectional track can be easily picked up and put down at will.
For a permanent railway, though, you should consider using flexible track. This can be bent to any desired curvature, and with it you can make your railway go where it should go, not where it may have to go with sectional track.

In designing your track plan, use the widest-radius curves your space will allow. A 820 mm radius (LGB R2 curves) might be considered a minimum (although sectional track will take you down to 645 mm radius - R1 curves), and 1200 mm (R3) to 2360 mm (R5) will give your railway a much more plausible look. Space is always a problem, so do what you must; but tailor your rolling stock to your curves. Very long engines and cars just don't look right negotiating very tight curves. When planning grades, try not to make them steeper than about 3 percent (3" rise over 100" horizontal travel). Steep grades are unrealistic, and they will severely limit your train length.