There are two buttons above the rear view mirror. When the motor is running press them one at a time - they will flash for about 2-3secs before stopping. When the ignition goes of the alarm is disable (used for ferry crossings etc) and then lock as Catman say with the key.
In stock at Eurospares, don't mess about - get OEM and the right one for the engine as the 4.7 and 4.2 engines have different filters. When my local does work on mine, I always order the parts to ensure I get the right quality of part.
I too live in Devon. There is very little here and you have identified the options….i have concluded that Emblem is the way forward now the SI has packed up its tools (hopefully temporarily).
There is a Ferrari indie in North Devon (Braunton) or Carrs in Exeter.
You are spot on, you did do it right and as such - this should and must hurt. Time now to build Sportsitalia V2 - Bigger and even better! Onwards and upwards