So I was just wondering if you really need to have the companions that you find in-game in your party. Because I have already created my own party members and would like to stick with these but I get a feeling that the companions you find can unlock sidequests or things like that and I wouldn't want to miss out on that..

So my question is if it's really neccesary to have these companions in your party while you travel or can I stick with my own companions without missing out on anything special??

Every companion has exactly one personal quest, though they're not really extensive.

Otherwise, you mostly miss out on some comments and party banter.

not necessary, but you will miss out on some story and quests if you dont use them