Hi,
I have 2 pairs of mandarins, lovely little birds, mine are kept in a run 20ft by 10 ft with a mesh roof, the pond is approx 8ft in diameter, and maybe 8 ins deep, there are also a pair of white pheasants in with them, both breeds tend to ignore each other and get on with life.
Mine are fed layers pellets, although I think I may try and get them onto waterfowl breeder pellets if I can find some locally.
I only got my mandarins in Feb last year, and to be honest they didn't really lay that many eggs, I incubated them but only one hatched and then promptly died 2 days later, mine didn't have the chance to go broody as I took all the eggs from them.
I'm sure you'll enjoy them when you get them.
Regards
Sue