Used Mr Surfacer Lacquer primer, main paints were enamels, lacquers and Future acrylic clear coats, tough combo. YF-19 parts fit very well with very minimal paint scraping, so it transforms fine but of course you should take it slowly.
The toughest part of the YF-19 transformation is seperating the 2 main nose parts, to make it easier you can just cut off those 2 tiny inner tabs , they turned out to be useless since the 2 parts lock in place fine without them.