Ok. Main thing is, you can DEFINITELY have your random gen 
I don’t know if you want to generate all at once, or as the player walks through, I think it’s the latter, right?
If your rooms are blueprints, and you are happy with that, I’d say, stick with blueprints, you don’t need to use streaming at all. You only need streaming if you have a LOT of stuff to load.
As far as passing info with an interface goes, you can pass all the same info ( and get answers ), that you can with a custom event, it’s just that a blueprint interface doesn’t assume what kind of actor it’s talking to.
You use custom events or BPIs just like you would if everything was in one level, because even if you’re streaming, you have to wait until the level is loaded before you can talk to anything in it. You can’t do anything before the level has loaded.
The garden maze I showed does things on the fly ( not pre-calculated ), as the player moves around, they are hitting collision boxes, which cause the blueprint they are currently standing in, to load a new random blueprint just around the corner etc.When the new blueprint is connected, there is some ‘dialogue’ between the two blueprints, because when the player leaves, you have to know which actors to destroy.
Am I saying anything useful?
If I’m still missing the point, there are two ways to go:
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You can focus on just the exact moment you’re having a problem with. Make it very simple, what exactly is communicating with what, where is your conceptual problem?
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We can hook up on discord if you like and discuss it, I have a server at Discord