I bought two batches of geese last spring/summer. First was Toulouse and Buff. I bought all straight run expecting to get mostly males, but I believe I received mostly females. The Toulouse were quite a bit smaller compared to weights claimed online. I processed 3, the heaviest of which was about 13lbs live weight, and they were around 6 months old or so. Overall, the meat quality was fine, but I was unimpressed with the size on the table, they were much like the "Young Goose" you can find at the grocery store.
The Buff females are smaller than the Toulouse. I kept 3 of those, 2 females and 1 male, which is what I happened to receive. The Buff male is pretty good size.
Subsequently, I bought 8 African geese, 4 males and 4 females that same year. I planned on processing 2 of the males, just never got around to it. This breed is also significantly smaller than weights claimed online. The females I haven't weighed, but I'd guess they're around 8lbs live weight if that. Very light birds. The males are a little more respectable, I'd say closer to 12lbs. They're about 8 months old at this point, so I don't expect they're grow much larger.
I received 5 embden males in December. One died in shipping, one died from unknown causes at about a month old. The 3 remaining are 9 weeks old or so, and are already bigger than my buff females and the Africans. I'm hoping I can raise these to > 20lbs live weight, I want a big bird for the table. Current plan is to raise them until around October at the latest, so about 10 months.
I also breed muscovies (well, I have some anyway, I don't have ducklings yet). The males dress out to 8-10lbs, basically the same size as the medium sized geese. The breast filets are much larger on the muscovies and the meat quality is probaby better IMO. They also only take 13ish weeks to get to processing size compared to 16-24 weeks for geese (or longer). The downside is, geese mostly eat grass, muscovies mostly eat feed, though they will eat quite a bit of grass in a tractor when they're young.
My plan is to keep buying different breeds of geese, I have French Toulouse and Romans, and more embdens on order. I'm going to keep the largest males and females and try to keep a bigger breeding flock. I think this will take a long time to come together fully.
WARNING: Graphic processing details below.
As far as processing them goes, I don't do anything special. I catch the geese I want to kill from the coop, and then I kill them elsewhere. I withhold feed from the entire flock the night before. I imported a dry plucking machine from Italy, and then I wax them. Part of the issue I have with this process is the dry plucker can rip the skin around the thighs and neck if you're not careful with it. The wound in the neck lets too much hot water/wax onto the neck meat and it turns grey and has to be tossed. I haven't sorted out the best wax temp/cooling time yet. Most of it comes off in small flakes and is quite tedious. Sometimes a bird takes 5 minutes, sometimes 30+ minutes to get all the wax off, but the wax generally does pull just about everything.
I also do muscovies the same way. I found that a 22lr to the head and then bleeding them through the mouth makes the neck easier to pluck and save. The muscovies are really tough birds to kill, if you slit their throats, they take forever to lose consciousness. Personally I find it completely unsuitable. The broomstick method is quick and easy on the females, mature males have really, really strong necks. The downside to this method is the bleed out into the neck cavity, and it's easy to pull their heads all the way off and make a big mess (again, if you're waxing, you don't want to expose the meat to the wax).
I watched a youtuber process some ducks, and he likes to 'pith' them in the brain and bleed out through the mouth. I will probably do some birds this way next, as it solves a lot of the issues I'm having.