I am developing a small computer program that involves moderately simple simulation of elliptical Kepler orbits for fictional, generated star systems. I'm doing this without much prior knowledge of orbits (apart from some basic equations) or astrophysics in general.
I'm attempting to create loosely realistic orbits in the sense that they are not all in one plane and that they are elliptical with the parent body at one focus. The program assumes there are only interactions between a body and the one it orbits. Planets do not affect other planets' orbits. All other forces are explicitly ignored with orbits following only Kepler's laws.
The axis of rotation of each body in this simulation will be static (ie. without precession) and the axial tilt will be pseudorandomly generated. I wish to align an orbit with zero inclination with the equatorial plane of the parent body.
The real question, then, is the following: are there are any important constraints to the direction of the axis of rotation of an arbitrary hypothetical body orbiting another hypothetical body of significantly greater mass that I should take into consideration when determining the axis and axial tilt?
Which is to say, can the axis of rotation of, say, a planet, "point" in any arbitrary direction?
(The axis can be assumed to be a vector in the direction of the north pole. The north pole is here simply the pole that is "above" the orbital plane when axial tilt is zero.)