I presume you already have the basics in place i.e. a secure, well ventilated shed or building (8ft by 6ft at least for that many), lots of grass (I guess half an acre or more) which shouldn't be too long, ideally predator proof, splashing water changed daily, grit and supplemental wheat/growers pellets. Beyond there's not much more you need to know, I think. Worm regularly, watch out for the ganders in breeding season and read 'Keeping Geese' by Chris Ashton
Enjoy them - my pair are brilliant, inquisitve, funny and bossy!
H