Some questions regarding language and linguistics

Oh hi.

I'm alive. Still.

As 1 of my subjects is linguistics and today I've just borrowed a book on English morphology (besides, I've been reading some articles/ essays... about linguistics as well), there are several things I'm wondering about:

1/ What is 1st language? Is it the 1st language a person learns (from parents) or the language that person speaks the best?

Let's say, a girl with Vietnamese parents is born in Norway. The 1st language she learns is Vietnamese. As she grows up and goes to school, Norwegian becomes her dominant language, she feels truly herself when speaking Norwegian and expresses herself best in Norwegian. So is her 1st language Vietnamese or Norwegian? Is 1st language the same as mother tongue? And is it the same as native tongue? Can we say her mother tongue is Vietnamese and her 1st language Norwegian? Or does her 1st language have to be Vietnamese whether or not she can speak it well?

The case of Vladimir Nabokov, he was 1st taught both English and Russian, and even though his parents were Russian, he was able to read and write English before Russian. At age 5, he started to learn French. And in his household 3 languages were spoken, so Nabokov used all 3 languages throughout his childhood till he became an adult and spoke all 3 languages perfectly for all of his life. So can we say he had 3 1st languages, or was it only Russian?

2/ What is 2nd language? Is it the language someone learns 2nd, after mother tongue, or the language someone speaks 2nd best? What's the difference between 2nd language and foreign language? If a person speaks a foreign language almost as perfectly as his or her own language, can it be considered 2nd language, or does 2nd language have to be 1 of the languages spoken in that area, or at least, it has to be the language spoken usually throughout childhood?

3/ What is a native speaker? I know a guy who is born in Germany and grows up in Germany, with a German father and a Vietnamese mother, who speaks German to him, besides, he never speaks 1 word in Vietnamese, is he a native speaker of German? When a guy is born in the US to Italian parents, grows up in the US and speaks some Italian at home but speaks English as his dominant language, can he be considered a native speaker of English? Or are native speakers only Americans who speak English both at home and outside home, to parents and to other people? When a girl is born in the US, then at, say, 8 or 9, moves to Sweden, and since then speaks both languages well, can she be considered a native speaker of English? How about a girl who has British parents, lives in, say, France, never spends any time living in an English-speaking country but speaks both English and French in everyday life and speaks them well, is she a native speaker of English?

And a girl born in Norway to Vietnamese parents, who grows up in Norway, speaks (limited) Vietnamese at home, speaks Norwegian as her dominant language, she's a native speaker of which language? Not Vietnamese, but how about Norwegian? Or none?

4/ What is the equivalent of "morpheme" or "morph" in Vietnamese in Vietnamese morphology?

5/ Is the Vietnamese language a suitable language for morphology?

(This, however, might be a stupid question from a person who speaks Vietnamese as a mother tongue and knows it unconsciously without ever studying it the way foreigners or linguists do).

6/ Put the matter of convenience aside, is the Latin alphabet, the abc system, suitable for a language like Vietnamese? 

7/ As far as I understand, Vietnamese is an isolating language, never uses inflection and doesn't have morphological marking of gender, number, tense, etc. And in Vietnamese I don't think I've seen derivation as in English or Norwegian, like "determination" from "determine", "modernise" from "modern", "glorify" from "glory", "teacher" from "teach", "drinkable" from "drink", etc.

So perhaps it means these characteristics become an obstacle in the formation of new words in Vietnamese and make the language quite unsystematic?

(This, again, can be a naive, ridiculous thought of a native speaker. Please forgive me for my ignorance.) 

Do these characteristics have an impact on our way of thinking, our logic?

(Considering Sapir-Whorf hypothesis I think "determine" is too strong a word. Language doesn't determine our thinking, but it does influence our thinking, though I must say it seems more like a 2-way process, since language is a part of culture and reflects the way people perceive the world and the way people think. To say languages aren't significantly different and therefore it's unnecessary to consider whether these differences lead to differences in thinking is also too extreme. For anyone who claims so, I would ask "But how many languages do you speak and what are they?" Someone might call this a fallacy in arguments, and it's true that linguists don't have to speak 5 or 10 languages in order to become a linguist, but if they speak too few, or if the languages they speak aren't very much different, I would say they should be careful when making such statements).