I've used the oils right on top of the acrylic paints and had no problem. I even cleaned the oils off a piece with turpenoid as I didn't like the results I was getting and it didn't do anything to the acrylic undercoat. I have not clear coated my parts before weathering, but I don't think it would hurt if you did. I do think I will do a clear coat over everything once the oils are dry and set. Just be aware that it can take weeks for oils to fully dry depending on how thickly they are applied. Usually when doing weathering, the oil paint is thinned out a lot with turpenoid which should help with it drying a little quicker. I have heard to apply thin coats and wait at least 24 hours between applications when doing different colors. Hope that helps.

Stephen