Hegel rejects the noumena/phenomenical dichotomy developed by Kant in his transcendental idealism and replaces it with his idea of absolute idealism.
This is absolutely right, but the important point here is that Hegel in so doing is not rejecting the things Kant put into the noumenal; he's rejecting the idea that there needs to be such an absolute distinction. This is because he also rejects the Newtownian description of the world.
My language choice above is very intentional. For Hegel, Newtonian physics provides a description of the world, one that he thinks is quite wrong as far as descriptions go. There are several places where he thinks its wrong, some of which are on solid Kantian grounds.
First, for both Kant and Hegel, "world" is for mind rather than an out-there. For Kant, access to the out-there the thing-in-itself is severely proscribed or outright eliminated. And this is where noumenal freedom happens for Kant. For Hegel, spirit can know things as they actually are -- in part because what we discover is that what we know is what we think.
Second, Hegel doesn't buy into Newtonian physics because he thinks physics is not the best way to look at the world. Here, the section in question is a part called "The Object" which describes objects in three ways: (1) physical, (2) chemical, and (3) social. The point being that each higher layer better describes things as we know them. This doesn't deny the lower ways.
Third, Hegel seems to have something personal against Newton (there was a recent question on this).
(1) Is hegelianism determistic at some point? Before the end of history? After? Both or none?
In modern language, Hegel's ethics would be considered compatibalist. Hegel thinks that the features of reason are determined but the rational use of will by spirit is free. This is basically the topic of Philosophy of Right. There's quite a few secondary sources on it like Aadrian Peperzaak's Modern Freedom, a volume by Thom Brookes, a volume by Dudley Knowles.
(2) If it is, how can Hegel make sense of an ethics under a deterministic worldview?
Hegel, like Kant, believes that moral action is action that accords with reason (For Kant, Groundwork, Critique of Practical Reason, Metaphysics of Morals, Religion). The difference is that Hegel's reason is in situ. He defends this account in several places (arguably) including around section 540 or so Phenomeology and as the central topic of Natural Law and again in Philosophy of Right.
But see above, the determinism he believes in accepts that physics can explain lots of things, accepts that reason decides right and wrong, accepts that we (as spirit) engage in reason over time and refine our understanding of right and wrong.
The process of refinement for Hegel happens in time.
(3) If it isn't, how does Hegel overcomes the deterministic Newtonian paradigm of the world without the noumena?
By rejecting the Newtonian description as a complete description of the world. Going back to "The Object" section mentioned above, Hegel argues that understanding the world as just physics is a bad understanding of the world and abstract in that it fails to understand the reality of chemical and social objects or the chemical and social aspects of the objects mind encounters.