Always make a pond as big as you possibly can. It needs to be 3ft deep in places - that's for the other inhabitants of the pond, so they don't get frozen solid in winter. And have a shallowly sloping end for things to get in and out. Definitely with an inflow and an outflow if you can arrange it, will keep it much nicer - ducks are mucky things.
If wanting to use a sheet liner, butyl is the best but expensive.
Flat stones round the outside (if using a liner) will protect the edge and quickly acquire moss between them etc so don't look so bad.
Your geeps or geese will keep the grass down, if it's cut to begin with. BH is right about the mess the pigs would make of an artificial pond
But. I'm not sure I'd start with Muscovies if you want a mixed flock of ducks and geese. The drakes can be quite agressive. My limited experience of those two young ones is that they picked fight with my hens and other ducks (literally, pitched battles!) and Goosepimple's fight with her ganders.
That said, Muscovies in themselves are interesting and come in many nice colours so maybe you just have mixed Muscovies?