You didn't mention if the Remote Force had the behavior set to Deformable or Rigid.
First question, why do the force vectors go in two directions? Because the beams are shearing and bending and the top is in tension while the bottom of the beam is in compression. You seem to call the four rods a "beam". If you had a long solid beam with a tip force, the material above the neutral axis would be only in tension. But you have a short beam made up of four rods, so they behave differently than what you were expecting.
Second question. Nodal forces depend on the mesh. If you have a cross-sectional area and fill that with 8 nodes, the forces will be very high compared with the same area filled with 80 nodes. You don't use the maximum nodal force to size the beam. The resultant force tells you the shear force and axial force. Knowing these values you can select a cross-sectional area that keeps the stress below yield by a large Factor of Safety.
Third question. The applied force has no Y component so there is no Y component in the Reaction Force. There is nothing to consider when sizing the beam in the Y direction.