Lots of questions here. Firstly, is it necessary to wire the frog of a point? Shouldn't the frog polarity be switched by the switch rail? Well, yes it should. But it didn't in two out of six cases on my so-far laid track.
In a spectacular and unprecedented exercise in forward planning, I had wired the point frogs in advance, just in case. So it's a matter of wiring them to a switch activated by the point motor.
Hmmm. I had planned to use a micro switch to drive the LED indicators on my control panel. Now I need another switch to change frog polarity. Is there a switch that can do both jobs?
Yes there is. Peco's PL15 switch does just that. But at £5 a throw it's too expensive to consider, with all the points I'll be installing (50+) over time. There is a DPDT microswitch that may work - a DPDT switch is basically two single switches changed by the same mechanical device (in this case, the point motor). I've ordered one from Maplins to test it, and then will source a cheaper version if it works in principle. (Maplins are consistently more expensive that other online sources such as All Components and Rapid.)