New to Koi

Just given 2 Koi. Know nothing about them. Not even what kind they are. They're 3" and 4" long, kinda brown or dark gray. I put them in my 90 g pond w/waterfall. Also have 2 Comets in there. First, I didn't do it. I know the ponds too small but... what can I do? Since I've got time before they outgrow my pond, (how much?) maybe I'll consider building a bigger pond. Also possible I can give them to our city's Japanese Garden. They've got lots of Koi in there. Anyway, how do you take care of Koi? Same as my Comets? Slightly different food I guess but the same otherwise? How about winter? Appreciate any input. Thanks in advance.

OK, got the skinney. No way can I keep Koi in my pond. It's way too small. Barely big enough for my Comets. I'll probably grow them until the end of summer and see if I can donate them to our local Japanese Garden. Dang... I was kinda lookin' forward to them. Don't want to hurt the fish though.
Cheers