I understand that the pilot needs to be VFR by the Initial Approach Fix.
You may be right but that is not necessarily how I would play it.
I would file a
Z flight plan i.e. VFR to IFR to VFR.
This specifies the two VFR transition points; usually as airway intersections or navaid names (cannot use "Upper Warlingham" on OFR flight plans
).
I would not go to the IAF, necessarily, though that is a reasonable approach (no pun intended).
Presumably this will always be lower than the minimum altitude for radar vectoring.
Possibly, possibly not. The radar vectoring area which a radar controller works to is not necessarily obvious where it lies.
If not visual by that point, but you were still higher than 1000ft above the highest obstacle within 5nm, can you desend lower accepting your own responsibility for terrain clearance?
Legally, I doubt it.
Whether it is foolish depends on the due diligence you did before flying
For example a descent over the sea, on the way to a coastal airport, is a good candidate for a DIY cloudbreak.
Obviously, doing this to say Biarritz is not quite the same as doing it to St Gallen (Switzerland)
At the latter one would need to be a lot more careful.
I think the intention is to use the EIR as an IR but with a higher MDA; typically 1000ft AGL.
Whether 1000ft MDA is valuable depends on where you are, and what time of the year. In southern Europe in the summer, during a nice high pressure area, it will be quite useful.