1) Does "military base" = "airfield"? i.e. for the purposes of determining strafe damage from fighters in close escort.
No, military bases are separate from airfields. If you look through your target cards, you'll see that some have a secondary target with type military base. This is the only way you can hit them. Military bases have a strafing penalty while airfields do not.
2) Some force cards list "Me 109 e" (i.e. 74,71,...) I know cp is channel patrol but what is e? I presumed it was Elite but there are no elite 109s...
This means the Me 109 is on close escort duty instead of hunting. At some point during the historical campaign, when bomber losses were getting too high, Hitler or Goering gave a commandment that more Me 109s were to be put on close escort, and the Me 109 pilots balked because that limited their ability to intercept British squadrons.
3)Channel patrol - can I confirm they only have an effect on a raid as the result of an event? otherwise they just head to the IF box?
If you mean they have no effect on combat, yes. Their effect for the Lion player is that's one less Me 109 gruppen you have to face in the Hunt box.
I might well spot the rules I missed on another read-through but can't see them at the moment. Had an extremely harsh raid day on the introduction scenario - I "forgot" southampton was in the LF3 range and left it completely undefended to 1 major raid followed by 2 consecutive follow-up raids while my patrols were concentrated further west. -13 VP in one day!
But now you won't forget it again. And 2 follow-up raids, whether you had patrols up or not, would ruin anyone's day.