Working up to 600-800 grit will prevent any scratches showing on base coat. The splotchiness, did you use a spray gun or can? Spray gun means the reducer wasnt slow enough so the paint is drying in mid air because its too hot. Can, ha well good luck. Also look up drop coat. When you finish your third coat of base,immediately throw a drop coat which will help metallic lay even across the whole panel and add consistency. Clear crinkle could have been from not waiting long enough with flash times (solvent pop).