I see there are animated PNGs here on Danbooru, but when I attempt to upload one it shows connection problems. The file is 13,8MB, but I've seen images with size of 44+MB.
Just don't do it. Generally speaking, we don't like pics with that size because the server isn't that good for them, and downloading things like that is a big pain in the ass.
I'd rather have original animated PNGs uploaded than destroying it by converting to GIF. But if it's not good enough to warrant the size I wouldn't bother uploading it at all.