If the grain exudes a milky substance, it is not yet ready. If the crushed grain has the feel of bread dough, it is just right. Harvest and spread stalks out to dry thoroughly. Wheat may be purchased in craft supply stores. If there is none on display, you may want to ask because it is frequently removed from the shelves since it is considered an autumn craft material.
Wheat varies greatly in size and thickness of stems and heads.
It is, therefore, impossible to give exact number of stems or lengths in directions. Work carefully, using your judgement regarding size and scale of the project as you proceed. The leaf sheath will pull off from the straw stem like a paper wrapper from a plastic drinking straw. Place in cold water until a stem snaps straight if you bend it all the way back on itself without cracking or breaking. Wall paper troughs from the paint store are inexpensive and very handy for this.