An impossible Q to answer because one does not have a long tape measure protruding from the front of the plane
but I suppose I would fly down to 3000m or so.
I would use the GPS OBS to find the airport, track in the extended runway centreline, and descend down to circuit height (1000ft AGL) at about 2nm. That is about 3700m away and one could descend down from there.
Enroute I am not at all bothered by IMC. VFR to IFR is one continuous spectrum and the flying is all the same. My nav is 100% radio nav.
For a departure, I like to see down the runway to make sure there is nobody on it, but would be happy to depart in about 500m, with a backtrack along the whole length. In the USA a zero-zero departure (Part 91) is 100% legal and I think it is also OK here, Class G.
I suspect that an experienced VFR pilot could fly an approach in zero vis using synthetic vision down to 150ft no problem
That's true but it is a bit of a psychological leap to trust it, down to 150ft visibility which assuming a ~3-5 degree approach is awfully close to the ground.