I top at the second internode and then again just before I flip so that the branches thicken up.
I don't flush and imo there is no point in flushing and may even be detrimental to your plant, but if you want to go with the normal paradigm then if you are aiming for little to no amber start flushing when the hairs have just started to recede and the trichs should be about 70/30 cloudy and clear, if you want a lot of amber then don't start till the hairs have all receded and you should see all milky white, a few will still be clear but nearly all white, and you should wait till you see that first hint of amber, 2 weeks later you should be looking at 30-50% amber.