18 Greens: methinks that "Most schools in the UK teach 2 stages ... " is possibly a little too sweeping a statement. I'd agree that it's common in the early stages of 12/13 to stick to 2 stages because the FI can be a little more relaxed about errors, but the aim must be to get the stude to full flap landings ASAP, and then to flapless.
As for gusty conditions, adding half the in-to-wind gust component to the Vat is all that's needed, maybe a little less flap if you want optimum roll control.
HFD