Yes,you're right.들 is emphasizing the plurality but sometimes even when you forgot to mention 들 like in 좋은사람들,but still the person you're talking to if he/she knows your talking about a group of people can understand and know that you mean the plural form of 좋은사람 without mentioning the plurality 들. but still good if you mention the plurality by using 들 it makes your content more clear. I hope that my explanation was helpful to you.

thank you so much!!

좋은 사람들과 translated into "with nice people" not nice person

if speak of just that person, you shouldn't use 들. 좋은 사람들과(X). however, if you want to say 'we', you can say either 우리 or 우리들

ah i thought 들 can refer to me and other person lol so in this case i dont have to use 들 if there were only me and that one person right?