Since massive and mobile figures can enter blocked terrain I guess I can also deploy them there, right?

Yes.

And they must if that space is the closest possible and the rest of the figure can be placed legally. And due to this I think the latest ruling/interpretation is that Massive effectively always needs to deploy on a valid deployment point, because it can be deployed on top of other figures - who are then Pushed.

Yes.

And they must if that space is the closest possible and the rest of the figure can be placed legally. And due to this I think the latest ruling/interpretation is that Massive effectively always needs to deploy on a valid deployment point, because it can be deployed on top of other figures - who are then Pushed.

Wow, that's some nice extra information!

Well, except when all active deployment points are on indoor spaces. Then the Massive figure is deployed to the closest legal exterior space.