Re: Spray Paint
Oil paint over an acrylic underpainting is a very commonly used approach. You can certainly get cracking when the acyrlic is not completely cured, which depends a lot on the thickness of application, the cure time, and the humidity. So, spray thinly if you use acrylic spray paint as an underlayer.
I haven't used enamel spray paint, so I cannot speak to concerns there.
Since most of the media used in art rely on mechanical bonding, the key for mixed media approaches is most often to have enough surface roughness in the underlayers to ensure the overlayers can fit into the bumps and cracks, and to ensure that there is enough curing. Oil media should almost always go on last (or at least on top) because oil creates such a smooth self-leveled surface that it is too difficult to find purchase. But self-leveling acrylics and hard-drying acrylic mediums can create this kind of concern too.
Comments and critique actively sought and much appreciated!
Rick. . . . . . . . . . . . . . . . . . . . . . . pigment storm fine art . . . watch the paint flow!