Germans being Germans, there is a systematic approach to Z-Scale layout construction.  If you are unfamiliar with layout design, you can use this approach to get running quickly.

When you buy an average Märklin starter set, there is enough track to produce a basic oval.  This oval has an 8590 terminal track, a single piece of 8500 straight track and four 8520 curves and six 8521 curves.  The mix of the two different curves provides the basis for an organized pattern of track extension that culminates in a completed layout capable of supporting several trains. This approach is often called SETTT, with the starter set having the “S” component and the additional tracks sets being “T-1”, “T-2” and “T-3”.

The 8198 (left) is for the “S” & “E” extensions, the 8199 (right) is for “T-1”, “T-2” and “T-3” extensions.  Originally, the completed layout using all of the extension sets was meant to fit on a toporama, producing this result:

Courtesy Märklin

This is, of course, the classic German style layout of the 1970’s; an orderly model train layout reflects the orderly mind.  Whatever nostalgia value this sort of layout might have, a lot of people have moved on to more interesting designs.  The literature that accompanies the extension sets now acknowledges this reality and the brochures show various interesting layouts created by different combinations of the extensions sets.

The track extension sets fit a general market need and they do have enough pieces and related parts to get you started.