Hi kodacolor,
Your corgi puppy must be very very cute!
>He wants to crouch down on his front paws look at us and bark, bark, bark.
This looks to me a gesture inviting you to play with him.
Is he wagging his tail (maybe he doesn't have much tail being a corgi)?
>For the past 2 days he has become very aggressive and biting and nipping quite hard
Again, this behavior looks to me as if he is playbiting you. If he was with his litter mates this would have been exactly he was doing with them. Puppies learn how to play (not to bite too hard, etc.) through playing like this. However, you should start teaching him not to put his teeth on your skin. When he playbites your hand, say "Ouch!" in a sharp and firm voice and ignore him for a few seconds. Give him a chew toy or squeaky toy instead. You will have to repeat this until he gets the idea of biting people is not acceptable.
In the mean time, I would like to suggest you handfeed him and/or putting your hand in his food bowl when he is eating. Sooner is better. Associate your hand and good things (food, treats, toys) to prevent any aggression to you and other human beings. You would not want any food aggression and it would be much easier to prevent/correct if any when he is still very young.
Good luck
