This is very true when I first started out I realized the enamel chews away at the fig and leaves it all sticky as stated above. Its all trial and error then!
When I used flat red I didn't get a tacky feeling on most of figures. I usually primed most of them with a flat bpach. The glossy enamel paints will definately leave the figure feeling tacky, and all will be that way on most accessories such as capes sheaths etc and anything soft plastic or rubber.
I've run into the eternally tacky problem too. Its usually with very soft plastic like capes or figures that are a bit flexible due to softer plastic. I actually ran into it on a ML Marvel girl's legs yet not the rest of her. Sometimes primer works but not always. when in doubt used water based. I'm using a cheap red primer for my deadpool but that's because I know the plastic is strong enough to handle it.