Dont sail there much but what I've heard is that la perouse is best in westerlies which have a bit of south in them, so for northerlies I'd say not all that good.
would be pretty offshore, but depend what your into. Back in the day ( before the birth of krusty I believe) the slalom guys used to sail there in noreasters and swore by it. I think they would launch from laper and sail down into yarra bay, pretty clean wind but real flat water. Hope that helps
if the wind is dead North the best spot in Botany Bay is Dolls Point. I have tried La Perouse in almost any wind direction but it only really works in SW to W. (Dead west however can be a bit gusty)...