It's definitely possible but you need to be constantly immersed in the language to be able to understand and apply the finer aspects of the language. Realistically, like with any other language, you need to speak and hear it regularly from a fluent source. If you indulge in good quality English you could easily be proficient as it is not a very hard language, but it certainly requires regular exposure so you can acquire the more trickier grammar.

I think it is possible for some people, but not for everyone. A lot of immigrants who come to the Netherlands will eventually learn the language perfectly on grammar/vocabulary etc, but they will never learn the correct pronunciation of a lot of words, just because Dutch has a lot of sounds no other languages has. This makes it almost impossible to learn. For example: because of this, most Dutch/German people cannot pronounce the th-sound (think, etc) in English properly.

Yes. It's definitely possible. I've worked with a number of second-language English speakers who have reached this level. Some immigrants to a country try their hardest to fit in and adopt the new language and culture. I've seen plenty of examples of this in Australia. The thing is, it's not easy and it doesn't happen by magic... but I've met the successes, so yes it's within your reach. :)

Actually Yulia, yes you can. However, you will need to use some "shortcuts" A clever tutor or teacher or "language partner" will be needed to get you started. For example, you need to be guided through the Dolch Lists of the most common English words. You need guidance into the study, not just of a single work when you enlarge your vocabulary, but the patter of the word, its most common synonyms and most common antonyms. There are others also.

Your question is a bit different, I suppose. Certainly reading articles and watching TV series is not enough. You need someone to explain to you the peculiarities of English pronunciation, the different positions assumed by the speech organs for each sound. Language learning is a lifelong process, it is natural that you cannot master the English grammar in two years. I studied linguistics at Moscow State University. And yes, I've seen people whose speech is indistinguishable from that of an educated native speaker.