Testing for PH is good advice, never hurts to give the sward the best chance of of providing as much nutrition as possible and it will change over time with lots of goose poo! Take multiple little samples across the area and mix in a bucket to get an average sample.
Grass is a crop and will need the odd overseeding every few years to keep the mix healthy. The goose poo may provide enough fertility but if you have free manure from other animals then spreading a light dressing around in spring won’t hurt.
Ultimately much easier and cheaper to keep it good than renovate damaged sward.
Not a poultry expert but my understanding is if you can leave it fallow from poultry for 6 months most parisites won’t be an issue. If that involves a bit of temporary fencing.....