spray coat over acrylic and oil paints

Hello! I would appreciate feedback on the following query; I have a plastic model ( Wingnut Wings WW1 German observation plane, to be exact ) that I have painted in Tamiya flat acrylic paint, followed by detailing in oil paints. Now, I would like to give it an overall semi gloss coating. Can I use a Testor's Dull Coat spray can, or do they make a semi gloss spray can? Will the spray affect the acrylic or oil paints in any way? If all is well with this method, should I apply decals before or after the spray coat? Are there any other brands of dull or semi-gloss overcoats in spray cans that would be useful that I am not aware of? ( I do not have an airbrush ) Many thanks in advance for any advice you can give me.