Using "Much - Many" In Positive Sentences

Hi All

I want to learn if we can use "many - much" in positive sentences whenever we want. As far as know, they are generally used in negative and question sentences. In positive sentences, they should be either part of the subject of the sentence. For example....

"Many of the guests liked him"

..... or it should be supported with another adjective such as too,so....etc. For example....

"There was too much sugar in my tea."

However, I sometimes see using of these quantifiers in positive sentences which are not compatible with the 2 criterias above. For example....

"I have many friends"

Is this sentence grammatically correct or does it have to be...

"I have a lot of/lots of/plenty of friends.

Thanks