It's perfectly fine to nurse you babe after having a drink. Alcohol goes into your milk at the same concentration it's in your blood.
I usually nurse my DD first and then have my drink, but if she asks to nurse while I'm having my drink or afterwards, that's fine too.
Basically, if you've had too much alcohol to drive safely, you should hold off on nursing the baby. This according to my aunt, who is an IBCLC.
Pumping and dumping is not ever necessary except if you're in a situation where you're not nursing your child for an extended period of time due to something in your milk, but you need to keep your supply going. Milk is continuously generated and is reabsorbed if not expressed. Once there is no alcohol in your bloodstream, there is no alcohol in your milk.