Vyurok said:
Is the following understanding correct? (...) you consider how the wave function (which describes the system's state in quantum mechanics) changes under an infinitesimal spatial translation and conclude that the generator of such a symmetry transformation should look like: ##-i\hbar\nabla##. And you identify this with the momentum.
Yes, this understanding is essentially correct. The operator ##-i\hbar\nabla## can be called the momentum operator, because - just like in classical mechanics - it was obtained by considering the effect of infinitesimal spatial translation on the system (the technical difference, of course, is that in quantum mechanics the state of the system is not given by coordinates and momenta, but by a complex wave function ##\psi##).
Vyurok said:
I know Noether's theorem in the following form (...). This is how I’m used to defining momentum, energy, and angular momentum.
Classical mechanics can be formulated neatly using the approach based on the Lagrangian or on the Hamiltonian. In the Lagrangian approach you have an explicit recipe for how to calculate the conserved quantities - the integrals of motion - using Noether's theorem. In the approach based on the Hamiltonian, you have to "guess", in some sense, the form of the conserved quantities - namely, the integrals of motion in the canonical formulation of classical mechanics are such phase-space functions that their Poisson bracket with the Hamiltonian is zero. In practice, however, you would not "guess" but rather calculate the conserved quantities using Noether's theorem, then go over from ##q##'s and ##\dot{q}##'s into the ##q##'s and ##p##'s, and substitute them into the expression for the calculated integral of motion.
Vyurok said:
But you are saying that these quantities can be defined as generators of the corresponding symmetry transformations. So, there must be some relationship between these generators and the conserved quantities along trajectories — but what is it exactly?
"Generators of symmetry transformations" is just the group-theoretic language for the conserved quantities.
I'm not sure at the moment about the second part of your question
@Vyurok, where you play around with matrices, but essentially there is also a way of obtaining the integrals of motion in the canonical formulation of classical mechanics by considering the
generating functions and the
canonical transformations (you can look up these "keywords" in the meantime

). Perhaps someone competent will jump in and explain this point clearly here.
Vyurok said:
Also, could you recommend good textbooks on quantum mechanics in general?
There is an entire thematic sub-forum here on PhysicsForums that deals with textbook recommendations, check it out:
https://www.physicsforums.com/forums/science-and-math-textbooks.21/
R. Shankar's "
Principles of Quantum Mechanics" seems like one of the good choices - the book is not too thick, contains interesting topics (in addition to the standard ones) and includes a self-contained mathematical preliminary on vector spaces. It is also good to ask your teachers about their recommendations.