This might be overkill, but you can think to different applications.
I can get around the inconsequence pointed out in comment by drawing a cylinder with h=0 to impost a 3d circle:
This solves the first issue of the question, getting a finite number of arrows.
The command \pstODEsolve can be called with an empty initial conditions argument. Then, it uses the last computed state ...
There is no viewpoint key in pst-3dplot. This key is defined in pst-solides3d. Instead, pst-3dplot uses Alpha (rotation of the horizontal axes around the vertical axis;default: 45) and Beta (vertical ...