Congrats on this exciting step, you will love it. Warning: you are undoubtedly already aware that a new "big" tank quickly begins to seem...less big. The same holds true for ponds.
When you are deciding what to keep, bear in mind that your pond will be much more satisfying if you can see the fish. Sounds silly, of course, but a pond...especially a planted one...makes them very difficult to see, other than an occasional brief glimpse of a flash of movement. I personally don't have much use for koi, but they have been bred to be observed and appreciated from above. You can't expect to keep more than two or three in that little pond, but that's plenty to make a nice display.
Suckers, catfish, weather leaches, darters...IMHO a complete waste of time. You'll never see them. If you want some little fish, Rosy Reds or Gold Medakas are easy to see and maintain. They're always on display and breed prolifically, especially the Rosies.
This is your first real pond; you don't need "something uncommon in the hobby". Anything will be new to you. Get something you will like without worrying about how many other people may are may not have it.
Oddball
posted and Ide, Bighead Carp, Silver Carp, and Grass Carp are illegal to keep.
