An estimated paint to primer ratio on exterior bare wood

I was quite skeptical about the paint and primer combo's, but Valspar gave me a couple of gals to try out. I was surprised how well it covered over dark colors. The down side was that it is not as smooth as regular premium grade paints. It seemed a bit dry going on, but that is because it is very high in clay content. I decided the best combo was to use it for the first coat and then use regular paint treated with Flowtrol for my finish coat. The application that I would never use it on is covering new drywall. I still prefer quick drying PVA drywall sealer. The paint/primer combo is too heavy and stays wet too long for new drywall, and is about twice the price of PVA primer.

The paint/primer should be fine, especially with two coats, but I typically begin with primer, as it seems (in my experience) that primer holds paint better and lasts a bit longer before requiring touch ups or repainting, and it's often cheaper to do a coat of good primer (match latex to latex, or make sure you follow the label if you use a different combo), then two or three even coats of less-expensive paint (paint+primer is almost always 2-3x more expensive than paint alone.

I wouldn't sand and re-paint, of course. You should be fine with what you have so far.

[Edit: one other note on paint+primer paints; make sure you read reviews or ask others about their experiences with the particular brand you're buying. A friend ended up with a patchy-looking paint job when he used one of the cheaper brands. I don't know if it was an isolated incident or if the brand is normally bad (or if he didn't mix the paint well!), but research before you buy.]