Most things are ok as far as art goes. It seems stuffed sharks are very in and shredded art is the delight to many folks with deep pockets. That’s the beautiful thing about the creative process.
However, for the purpose of durability and thinking about the more practical aspects, such longevity of your art there are many considerations. You want your art to be around for as long as possible, not just a few months, understanding how the different media interact is key.
Whatever the surface you are applying your art to understand your different media, how they interact with each other and how they interact with the paper, canvas, or other surface on which you are working.
When using acrylic paint on top of oil paint, most people seldom do this, because of the limited adhesion qualities. With that said, I often layer them as a medium, (say for a collage. Oil paint generally works better on the surface and gives it usually a more vibrant color. Often they compliment each other side by side, but each to their own.
One product for sealing various layers of paint is to use a spray-on fixative called Crystal Clear by Krylon. It serves as an acrylic coating spray that provides a permanent protective gloss coating that refuses to yellow with age. Winsor and Newton also sell an Artist’s Fixative picture varnish, prices for both varies.
When starting out some artists, myself included would use hairspray. I don’t recommend this. Hairspray is water soluble, which means moisture in the air or humidity would cause it to be sticky giving it an adhesive quality. Dust then sticks to the surface of your art once it is sprayed. The other reason hairspray is not intended for art projects, is it doesn’t provide a permanent coating. The coating will eventually wear off. Also owing to oxidation it will yellow over time. Nobody wants their art to be the color of urine over time, yuck!
One other solution is to buy artists’ quality acrylic paints. These don’t need to be sealed as it’s permanent, doesn’t chip when dried and is water proof. Make that shift from “craft” acrylic paint to art quality paint, it’s worth it!