Working in civil aviation, nitrogen filled systems are common place, as Richard suggests a accumulator like you describe on the Saracen I would suggest checking px every couple of weeks , what px are they being charged to? Ques 5 yes to lose all px in a year strikes me as possible , only way to know is charge them fully then monitor leak down rate , u can check for leaks wild a soapy water mix if theirs a leak u will see bubbles