Honestly I don't think those things are that big of a deal. yeah it's annoying, but very few people are going to be setting up on new devices often enough for the verification thing to matter (also it's only needed for encrypted chats, which won't be most of them) and most discord users either don't care about emojis or use whatever is available on their server as part of the server. Just letting rooms (probably need a way for all rooms in a space to have them too) have a set of custom emojis tied to them should work for most people. for the people who do care about emojis and stickers, they can have any emoji or sticker they want.

I think the main issues are things like slow load times and trying to keep every room loaded at all times. the first can be alleviated by going to a less popular instance or by fixing the second. most people won't trust instances other than the main one for a while bc they are new to the federated stuff. The second can be fixed by just not trying to load every room. you still need to check for new messages every so often but that doesn't mean they all have to be loaded at all times. I'm also pretty sure you can turn of the verification thing in your instance account settings.