Pronouns are words that replace nouns, therefore a nouns can be pronouns. I wanted to leave it up to you.
"I'm watching" implies that you are watching at this exact moment. "I've been watching" implies that you have watched something on a regular basis. I'm not sure whether it is grammatically official, but this is just how we talk
. There is a similar thing with past tenses which can be a little tricky. "I did it" and "I've done it" for instance, the first one refers to something that happened in the past and it is now over, the latter one has to do with something that happened but still has something to do with the present, as I said, I don't think it is official, but it is how we roll bro
I should use (should "have" used exists?) this kind of sentence ("I've been").
I've no phreaking idea of what you meant by that. If what you meant was if the verb "to have" can ever be used as synonymous with "to exist", then the answer is no. Always use "there is" or "there are".
Try to join an English speaking forum, and please let them know that you are trying to master the language, or they might think you're American
Another advice is to always proof read what you write. The English language has a way of messing with your brain with all the your, you're, where, were, two, to, too, bye, by, buy ...