Hi bojan,
As for the interaction to measure the gravitational wave, because gravitational waves have such a weak coupling with matter, that is what made the measurement so incredible difficult.
Weber's principle idea was that the gravitational wave would 'ping' one of the resonant modes of the bar, and then he would readout the 'energy/displacement' of that resonance. That made these bar detectors 'resonant bar detectors', looking at gravitational waves around 1000 Hz (actual frequency depends on the resonant mode of the bar). The signal could be followed for maybe 10 Hz to 20 Hz, and then disappeared in the noise.
The LIGO detectors, are 'broadband' detectors, and are able to follow the gravitational wave from 10 Hz to 8000 Hz. The GW150914 event was a signal from 35 Hz to 150 Hz, over a period of 0.2 seconds.
As for more detectors, they are coming online (Virgo early next year and KAGRA later), just takes time
I am all for a detector in Australia... would be nice. That would primarily help with the sky localisation for EM followups.
Also, LIGO made an initial faq page which may be of interest,
https://www.ligo.caltech.edu/page/faq