[MINIMANIAUK]

The cheapest solution is simply to raise the rear of the bonnet by an inch -but this will not look good.
for vents to work they need to suck air out from the bonnet ,they do this by having a differential in air pressure beween the under bonnet and the bonnet surface
The surface pressure varies across the bonnet and the prime spot is likely to be around the area of the existing scoop (it is a curved surface before the bonnet flattens out) but it would not be the easiest position to actually fit due the curved nature, however the further forward the better,and following the airflow from inner to outer (again not the prettiest!)
If far enough forward it may also be possible to direct the radiator ,expelled ,heated air out the vents too.
a small vent just behind the intercooler would help too.
its all a case of form or function,and even if not the perfect windtunnel tested position they would still work.

 

[MINIMANIAUK]

The under bonnet heat comes from different sources ,the engine,the exhaust and the radiator and intercooler
The radiator and intercooler add significant heat ,but they are related to speed -the faster you drive the cooler the outlet air becomes ,simply due the amount of air/second passing through the rad increases with speed -
over 40mphish the under bonnet temps will reduce ,louvres will help release hot air from stationary to this speed , it is still possible to have high boost and low speed.
The oil cooler is not only to keep the oil to a level of temperature for prolonged oil life --it is for removing heat from the engine
if your oil temp is increased by 10 degrees , then 5 liters oil have been heated ,that is a lot of heat energy . this heat energy has come from the piston top ,rings, combustion chamber,head,valves etc -this heat energy is a lot more that 10 degrees in those areas,but results in a 10 degree oil temp rise
if you are at a steady 90 mph you will get a certain oil temp an increase in speed to say 110 mph the oil temp will rise say 15degrees -this is due to the increase in power the engine is providing (to overcome wind resistance)and an increase in rpm
likewise the increase in boost pressure gives more power and more heat in the top end of the engine and that is why I suggest an oil cooler.
a little extra oil quantity wont harm either

 

[MINIMANIAUK]

For oil analysis try and get a sample from half way during draining and avoid the lowest oil in the sump and the last oil in the sump,
You can tell a lot by simply smelling the old oil for fuel in it or burnt smell ,and looking at its condition
Around 140 degrees C synthetic oil starts to have problems so a bit over the normal needle position should not be a worry oil condition wise