They can use whatever license they want, but if they trap their users like that (not everyone can pay, not everyone can self-host), then they're not truly Libre, at most, they would only be so in words, or just lip service, if at all.
About the features, there are ridiculously low character limits, also ridiculously low filesize limits. The part of emojis, stickers and banners is not that important, although the fact that both Stoat and Matrix lets you do these for free (and they have pretty high size and character limits without charging you for that) is just better. Stoat's not hard at all, and with Matrix, just point it to unredacted.org and that's all, you can create a community (that's the word for "server" in both Stoat and Matrix [along with Space here, though]) pretty easily.