Here are some thoughts on your wall on slab problem;
1. The wall should have a metal flashing from 6" up on the inside, under the wall, and 6" down on the outside.
2. The plate under the wall should be made of treated wood.
3. Yes, the ground should slope away from the house.
4. It may be necessary to make a swale ( a ditch with gently sloping sides, with an open end ) along the house to drain the water away.
5. The concrete chunk you hit may be the footer.
6. Re-do the drywall inside and the vinyl siding on the outside.
Let us know how it works out for you and thank you for the pictures, they were a big help.