The brightness you describe, I think it is what I saw with my friend. She was smiling, too.
I think your brother wanted to let you know that he is not dead and doesn't want you to be sad because of him.
The rest... I am not an expert when it comes to dream symbols, also, they can be very personal.
He did not want to talk about the drugs that caused his death and went with you to a party... could mean he wants you to keep the pleasant memories and let go off the rest, maybe...
"sometime after we are finished" also could mean that he will contact you again or that something will happen in another life... or maybe he wanted to say "do not care about me too much, go on with your own life instead"?
The tubes somehow make me think of veins, and the box of a womb... like he is preparing his next incarnation...
But as I said, dream symbols can be very personal.