Try putting the window all the way down then holding the button for 10 seconds (I think it's 10 anyway). Then put the window all the way up and hold for 10 seconds. Try that a few times, and if that doesn't work lube the mechanism and/or the rubbers which run along the bottom of the window frame.
If I'm understanding correctly, you can buy a used ecu from a 197 and send it and your current ecu to someone who can swap the immobiliser over from the current ecu to your 'new' ecu. You'll then have a standard unlocked ecu which can be remapped.
Later gearbox from a 200 is slightly better but not by much. Other clio and megane gearboxes fit but are completely the wrong ratios to suit the engine and will ruin acceleration.
Stones/debris can absolutely cause the aux belt to come off, which in turn can take the timing belt with it. Both Pure Motorsport and AP Motorsport sell covers to protect against this.
Unfortunately unless you can prove a parts failure (tensioner etc) then I'm afraid you're left with the bill.