Wow, sounds like these could have greatly varying effects on the rest of your story!

I'm afraid #1 and #2 might bother me (I appreciated when the Magician's Nephew cleared up the use of English in Narnia, for example, but less than that would be annoying. And why does this character come from our world in the first place then? As readers from our world, we're already experiencing the book as a portal (to some degree at least, depending on the immersiveness of your world).
#3 Sounds appealing to me in its authenticity, but also difficult. As in, you will be limiting how well this character can communicate and understand things for a good while (and maybe it works out to skip ahead to the point where they can understand things better, though that seem unlikely).
#4 seems like it depends mainly on the tone of your story, and could easily be annoying or natural. Do you want magic to be an integral part of the world entered through the portal? Are there other kinds of magic that are simliarly used? Do they get explained or have systematic rules?