In English, a collective noun is a name for a group of people or things such as "family," "class," "pack," "bouquet," "pair," and "flock." Collective nouns usually take a singular verb, because they are singular in construction, but they sometimes take a plural verb.
Similarly, there are English nouns that are plural in number but singular in meaning, and they take a singular verb: "Mathematics was my favorite subject in school."
In most cases, yes. I am a native English speaker and those two sentences are different ways to express the same idea. But, "It is crowded here" is used more often with a negative connotation. Whereas, "There are many people here" can mean a positive good thing (like for a fund-raising banquet for example). It can differ per situation whether either are positive or negative. Did that help, or was it more than you wanted to know? ;)
I respectfully disagree. There is no hard and fast implication that one translation has a negative connotation and the other has a positive one.
Also, I would just like to throw out that as a "thank you," an upvote should be sufficient. In the Comments section, there's too much to read that's just not germane.