paint then seal with a gloss so the decals will go on nicely. then you can weather. But different effects (filter vs wash) work better using gloss or dullcote, depending on what you are trying to do.
his is my goto article since I'm a hack and still learning: http://www.ipmsstockholm.org/magazine/2003/01/stuff_eng_tech_afv_weathering.htm
There are as many ways to do weathering as there are members on these forums. :-)