I am making some Christmas ornament to sell at a schools faire. I need to add glitter to some flat objects and I thought to just buy PVA (the usual gloopy kind) glue to add it? I was planning to apply it with a paintbrush. Will this work and if so, should I water it down or leave it at the same consistency?

The usual PVA glue works fine enough on the PLA plastic objects and you can apply it on the objects in the similar consistency as obtained with the help of a paintbrush.