I've just done exactly this. I opted to pick up G2 & even some G1 components second hand to keep the costs down (we were kitting out the entire band with individual stereo mixes, so buying brand new G3's for everyone would have got ridiculously pricey). The one thing to be wary of if you're running multiple units is Intermodulation, which is effectively frequency dependant wave cancellation, it can cause unpleasant noise and interference between units. The more units you have, the more it is likely and the more you will have to frequency plan. I would also recommend an Antenna Combiner if you're using multiple units, we have had quite a few issues with drop-out.
Also, make sure you learn a little about legal bandwidth in your country. In the UK after the Digital Switchover, Ofcom decided to sell off the bandwidth and re-shuffle in a bid for European Harmonisation, but didn't consult the Broadcast industry before making it's final decisions. Eventually after a lot of lobbying, basic user bandwidth is now allocated to Channel 38 but requires a yearly licence to be purchased, there is also free bandwidth on Channel 70 but none of the manufacturers make gear that uses this frequency any more.
The direction I took with earpieces is to get some good quality generic units first as a baseline, and then see if it warranted upgrading. We're currently running on a collection of Shure 215's, 315's & 310's. Popular opinion and my experience is that the 215's are actually better than the 315's if you're performing guitar based music, 315's are potentially more accurate but 215's sound much more exciting. Probably a personal taste thing to some degree.
