Hiya,
if you want to keep your ui-settings, dont forget to copy the contents of your [old servername]_[charactername] folder (found here \Horizons\prefs) into the folder
unity_[charactername] (i think it will look like this). If you do this after the first time you logged into Unity with that character, you are certain to get the right folder. Maybe they changed the hotkeys again, but at least you see the old icons and your other settings will be the same as before (like chat settings etc.).
see ya soon
edit: you can also delete your old world caches to save some space, just be sure NOT to delete sector_default.def file in the world_cache folder