The thing that got me started in this hobby 3 years ago wsas a 100g pond I 'built' (well dug the hole anyway) in my ex-wifes garden. Had a dozen fatheads (bait fish from the local gas station) and some rosie's (feeders from Petsmart) but they were not much to look at so I bought a comet and 3 shubunkins at Petsmart to surprise her. Following year came 2 butterfly koi.
Now 3 years later there are still some pretty big fatheads and a couple of rosie's, the Comet is about 7" long and has the build of a heavyweight boxer, the koi are about 8" and the shubunkins, well they're almost as big as the comet. They stay in the pond all year, last winter I broke ice 5" thick to feed them. When I 'visit' I just sit next to the pond and they all come to that side of the pond and watch me (I know they're just waiting for the food but it does feel like they know me). Great place to sit and let the stress of the day fade away.
Project this winter is a 15' dia circular pond with a smaller 'satelite' pond and waterfall, give my 'therapists' some space!