At the basis of yantra operation is something called "shape energy" or "form energy". The idea is that every shape emits a very specific frequency and energy pattern. Examples of old believes in shape energy are the yantras and mandalas of eastern philosophies, the star of David, the five pointed star (pentagon), the Christian cross, the pyramids and so on. Certain 'powers' are ascribed to the various shapes. Some have 'evil' or negative energies and some 'good' or positive energy, but in YANTRA only the benefic and harmonious energies are used. When one focuses on a yantra, his mind is automatically "tuned in" by RESONANCE into the specific form energy of that yantra. The process of RESONANCE is then maintained and amplified. The yantra acts only as a "tune in" mechanism or a doorway. The subtle energy does not come from the yantra itself, but from the MACROCOSM. Basically yantras are described in the vedas as secret keys for establishing RESONANCE with the beneficial energies of the MACROCOSM. Very often the yantras can put us in contact with extremely elevated energies and entities, thereby providing invaluable help on the spiritual path.

It depends on the size of Yantras, material of Yantras, work of Yantras. In most normal situations yantras get fully activated within 40 days of installation and continue to increase energy thereafter.

Yantras have geometrical and mathemetical rhythm of natural forces to attract and absorb cosmic energy. Just like your TV or radio antenna works with the elements for better reception of frequency.

Yes, the bigger the yantra the more is the impact. For smaller rooms, small size is sufficient.

Yes, you can. Ancient texts do not mention any such taboo associated with yantras.