So as I make my way through the story, I've come across several groups and each of these ask me to join and want me to do various things for them. Which is fine... my primary question is do these factions/side quests affect the main quest... OR does the main quest at a certain point lock out any of the factions? Basically, I just want me first playthrough to focus on the plot, then I'll worry about all the neat side content the next go round.

Based on how things are going, I'm getting the sense that I'm going to have to make a decision about how things go down and I'm quite sure all my new friends will be involved... and I doubt everyone is going to get their way.

Other question.... is the dang BoS invading or what is the deal there? I haven't associated too much with them, but I know they keep showing up everywhere I seem to be.

Thanks in advance, and please try and avoid spoilers if you can!

This is my question as well. Will proceeding with the MQ after a certain point lock me from other factions? Or am I able to do all of them including the main quest?

As for the BoS, I won't spoil much but...let's just say they're there to enforce law and order to the Commonwealth as per their own vision. And on occasions, you'll see them do battle with random enemies in the Commonwealth.

Yes the main quest will lock out certain factions depending on your choices

It will be pretty obvious when you reach that point though, and you will even get a pop up saying that if you go through with this mission you will be an enemy of the opposing faction.