I have a character who immigrates from his native country when he's eleven. He has no prior knowledge of the new country's languages, and the alphabet and lingual group are different from his own, so he's starting from scratch. His native language is spoken at home, and he reads in it extensively (though less as he becomes literate in more available languages). There's no public education, but he's tutored with a small group of native speakers, and expected to do the same work with no special guidance.
He needs to achieve literacy and fluency in three of the country's primary languages, and grounding in several more (primarily for research purposes), by the time he's sixteen - at which point he enrols in university, where it's assumed he'll have been multilingual all his life. His native country is far more monolithic and isolationist, so he'll be monolingual going in, and completely unprepared in education or expectation for learning new languages or being a lingual minority.
1. When could he be expected to achieve fluency and literacy? Would he ever be as fluent as a native speaker? Would the number of languages affect this? Is he likely to mix them up as he learns them?
2. Are there stages he would go through, learning to speak (going from quasi-Germanic to quasi-Romance)? What's he most likely to mess up? When could he be expected to speak in broken sentences? In full, correct, but awkward sentences?
3. How long would it take for him to have a passive understanding, in listening and reading?
4. Would he remain more aware of the structure and mechanics of language than a native speaker, or would he internalise it eventually?
From what I've read, there's a huge range this could fall under, and it's all very hedgy as a result. What would be average?