I would say it depends on your speed.
While climbing the WEP+100% radiator should be the most effective way.
At top speed most, if not all of the extra power from WEP should be eaten up by the increased drag of the cooling flaps.
In general I would not bother too much with MEC as a sim beginner. There are enough (and more important) other things that need your attention. You can open the radiators to 100% while takeoff and climbing and then set it back to auto when you have reached your altitude. But that´s all you need for the first months.
@topic:
For props I would say, try the FW190s. (Especially the D-9)
The controls are super precise and responsive, you have good weapons and plenty of ammo. But they are no turnfighters, so don´t even think about pulling against a Spitfire. Stay fast, dive in, climb out, repeat.
If you want a turnfighter, try the Yak-3. Its a little monster at low altitudes. Easy to fly, good cannons.
As said before, spitfires are super wobbly, so not the best plane to start.
You should test fly some planes, get a feeling for them and then choose those, that feel good for you.
( e.g.: I don´t like how Bf109s or P47s fly. It just doesn´t feel good for me.)
For jets I would recommend to begin with the F-86 Sabre (The german CL13 MK6 is the best imo. You outturn and outclimb almost everything) But other Sabres will also do.
They have great cockpit visibility compared to Mig-15 and -17 and plenty of ammo, so you can practice more.
I wouldn´t go higher at the beginning, as you need to build up situational awareness before you add more distractions like Radar, RWR and so on.
So set up your Track IR.
The most important thing in sim is observing and understanding your surroundings.
