You'd need to find the wiring diagram (look on ebay for elsawin) for PFL and FL pumps and see whats involved. If theres enough similarity you might get away with simply adding pins to your existing harness, but if the harness is majorly different you'll be having a big headache unless your good with wiring.
The boot release is controlled by the pump. The "open" buttons goto the pump, and if the pump is happy that the boot should be opened (ie the car is unlocked) the pump fires the solenoid.
You'll need a 3 button fob most likely yes, but you may find your existing two button fob will work ok.