The only restriction, that I’m aware of, is that the Event is only available in January.
Note: The Achievements are global. I’m not sure if the Pets and Portrait Frames are available immediately for both Season and non-Season. If not, they will carry over, including the Red Soul Shard Legendary Gem, if you want to do this with a Seasonal Character.
Sorry I’m “late to the party”, but if you need some tips, you might want to look this over: [SPOILER] The Darkening of Tristram Guide
Just throw an emoji on the end of it. (The characters that make up the emoji count).
For example:
“Great! Thanks!” = 13 characters. (I don’t think spaces count).
= 9 characters. :ok_hand:
So, “Great! Thanks! ” = 22 characters.