very well said philter
I was going to pretty much say the same thing.
Nothing personal, and do set your goals for these birds. BUT everything you listed is NOT for beginners. Comparing care levels for these species of duck geese and swan to proper care for calls will get the phone hung up on you when talking to these breeders.
No, do not keep these together with each other, near any form of domestics, or on open ponds.
Very few brant geese are kept in captivity, they are a northern species and a salt water species, so they will need to be kept in pristine high flow crystal clear water in pens, the $1500 + the pair cost will be nothing in comparison to the money spent to properly house them.
Pygmys depending on the species can range from $3000- $5000. There are even fewer of them, pretty much you're going threw the Lubbocks if you do ever get any. They are contracted out with a lot of the zoos that have them to get their excess stock back, pretty much AZA breeding loans from Sylvan. THEY WILL NOT SELL to anyone who is not 100% seasoned keepers of high end specialty species of waterfowl, period.
when paying this much for a single pair of birds, yes a private pen per pair is well pretty much mandatory.
Bewick's swans will be about the cheapest of the species you mentioned, but finding them will be a nightmare as very very few breeders keep them as well. Start with black or white mutes, then if that goes well, I'd suggest going to Trumpeter's or maybe whoppers
The only place you are going to learn about these species is on the GBWF site
The Gamebird Breeder's and Conservationist Gazette
and The American Pheasant and Waterfowl Society (A.P.W.S.) magazines.
look up that site, read a lot first before you ask, they will black ball you pretty quick if they feel you are asking in over your head questions.
Subscribe to those magazines
and most importantly, and pretty much mandatorily, buy you a lot of the common waterfowl and get some hands on experience with keeping them first. There is a massive difference in keeping this stuff compared to livestock and domestic waterfowl. If you cant keep and successfully breed these, than for the birds sake and your wallet, pass on these super specialty species. There's a reason only 3-4 people in the country have them privately