Blocking and bodywork

Yes you will start to level filler with 36-40 grit, sometimes even cheese grater, and it will leave filler rough, anyplace it hits anything but filler, 36 grit it will leave scratches in the METAL. Those scratches in turn will have to sanded with 180 to get rid of. So yes, 40 to 180 on filler, then hi build primer, you looking to make a smooth surface to seal and topcoat. The hi bld primer will only do so much, so scratches need to be gone before that primer. There is a polyester primer that is almost like spraying body filler, it will cover some sins but who needs 1/4 in thick primer!! LOL
Since I am no bodyman, old and woreout and don't have a $3000 compressor, I figure when I make a mistake, I can simply correct it. So can you! Let the process of dirty hard work, become as fun as you can make it!!!!!