Congratulations! And yes, you do have your hands full!
The first thing to look at with poo eating is his food. Sometimes a kibble doesn't really agree with a particular dog and their body does not absorb all the nutrients they need...so they eat their "protein packed" poop.
If you're feeding a really good quality food, then he may just like the taste of poo...Mmmm Yummy! There are products available at pet supply stores that you sprinkle on their food that is supposed to give their poo a bad taste. The only other solution I know of is to follow them around with a scooper and clean up right after he goes potty.
I wouldn't worry too much about the weight as long as you're not planning to breed and then you would need her to be within the breed standard weight. Average Corgi puppies should weigh about one pound per week old up to about 20 weeks. Charlie was only 5.5 pounds at 10.5 weeks, so I was afraid he would end up tiny. He may end up small still, but he's a "whopping" 22 pounds at 10 months. He caught up a bit, and still has some growing to do. As long as your girl's healthy, I wouldn't worry to much right now.
Congrats again! I'm expecting some great stories from you and your crew!