nummer is a bit of a false friend. In Swedish, it refers only to a 'nominal number', that is, a number used for identification. So number 3 is nummer 3, but a number of people is ett antal människor and can never be translated with nummer.
Another example where nummer is used is in phone numbers, telefonnummer, those are also used as identifiers rather than quantifiers.
Can "av" be included here, or simply "antal manniskor" is a phrase meaning number of people?
You can't add av. The construction without a preposition is the normal way, like en kopp kaffe = 'a cup of coffee'. When av is used, it is more for materials, like ett hus av sten, 'a house made of stone' (stenhus is a more frequent way of saying it) or something that is meant to resemble something, like en bild av en blomma 'a picture of a flower'.
I know I didn't even ask a question but your comments always answer questions in the back of my mind and the examples help as well!! Thank you!
So for exemple, if I mean to the firemen I say Vi har ett stort antal brandmän (we have a big number of firemen) <in that place>
Difference between antal and mängd? Could this be ett stort mängd människor?
Antal is for number, mängd is for amount. For people/människor, you could really use either depending on whether you treat it as a number of people or a mass noun.
For the individual word the sk sounds like hw (which i thought it was), but in the sentence it sounds like sh. Which is it?
Could "antal" also be translated as "share of"? (Sounds like the German "Anteil"...)
"A large number of human beings" was marked incorrect, is there a particular distinction that anyone knows of (person vs. human being)?
I'd say they are the same,... except would non-human beings be people? Is Yoda a person? Spock? Some would argue that human being is more specific than just person. Oh, and person is actually a Swedish word too, in the SAOL.