So I've advanced the main quest to the point where I'm supposed to travel into the glowing sea, I've completed the meet and greet on the Pryden, and I'm at the point in the Minutemen quest where I'm to take the castle. I haven't touched the railroad yet. I'm thinking my character will join the Beotherhood completely but I'm not sure. At what point do I lock out the other factions?

No spoilers please, a simple you can keep going, soon, or you better start the others now will suffice.

Don't worry, you get a warning about it when it's to decide "Do I want to make them my enemy". Unless you attack them or say the wrong thing to a leader. Then you're basically screwed. And that could be anytime you're talking to them.

This.

A clear one I hope and not like "settlement is under attack" ?

Oh, yeah, pretty darn clear. Message box that you have to hit "ok" and everything.

Thanks you. That should do me just fine.

Good and thank you... Unless sarcasm