Then there's one thing you're forgetting: actual modern Icelandic and fast-spoken Icelandic. I'm no genius in the verbs and tenses and whatnot but I can tell you this: Icelandic gets harder by the minute.
English is influencing Icelandic very much in the modern world (especially for teens and kids with phones) so it becomes harder, every minute, as Icelandic adaptations of English words (though mostly swear / profanity words).
Fast speaking is also a thing. You might study for months learning a few sentences but when your visit to Iceland finally comes you realize no one understands you; because Icelandic words are always merging and being shortened. A sentence or phrase might have five words but you merge two together and one is so short it barely makes a sound so it ends up sounding like three words.
Also, don't be fooled by the names of volcanoes or glaciers; we Icelanders love to mess with foreigners trying to say Eyjafjallajökull. I say this as a human born on Earth on Iceland and have lived in Iceland my whole (miserable) life.