It's my first time playing. I wanna stay at Minuteman. Yesterday I got a radio signal, got a new quest and helped some guys (Brotherhood of Steel). I did the quest that I had to follow Priston, kill those robots, now I'm back at their base. He's asking me to join him or nah. Will it effect Minuteman? Is it good to do? Someone please explain.

(Btw I can't say no. When I say no he says think more so all I can do is saying yes. So the quest is not ending. WTF. Should I join? Other ppl from internet says that I can kill them but will it effect the rest of the game, or bug it?)

You can join all the factions and it wont really effect anything until you get to a certain part of the main quest, but the game will warn you at that point anyway

I heard that those 2 factions are important. Like they have their own ending, bigger quest lines etc. Where do I need to stop while being BoS ? I mean when should I say no or something

Correct me if I'm wrong. I can join both Brotherhood of Steel, Railroad and Minuteman and do ALL their quest? I want to do as many quests as possible with all the factions, before having to choose. So unless I'm on that "certain part of the main quest" I can do whatever they ask me to?

Yes you can!