Heh.
I start building Ints in 2x parallel runs until I have 2 in every airfield Ger starts with, as well as 2 airports I build starting at game start. Those two fields being one at Dortmund and one at or near Dresden.
The interceptors at Dortmund are set to one province patrol over Dortmund because that place is a strat bomber magnet. The one I build at or near Dresden is just because that area looks so empty and... Dresden was a bomber magnet irl, and you never know when history will repeat.
I have found that pairs of interceptors are enough during the first year of war. I also have enough spread out that when a pair of interceptors starts getting beat up, I can simply cancel it's intercept mission and assign that area to a nearby airfield that was holding in reserve. This lets me keep fresh air fleets in rotation.
As the war progresses, I can regroup my air fleets into whatever size needed, and have enough on hand to spread out to cover conquests.
Early 1940, usually, I stop building interceptors and start building multi-rolls which I use in both ground attack and air superiority missions.
This method ain't min/max, and it's probably not all that wise a use of IC and resources, but it's a habit, and it seems to work well enough for me.