Sorry you had to go back into the hospital for dehydration. That happened after my ileostomy surgery, too. They are so active at first that it's hard to keep up with the fluid intake by mouth.
I had surgery 2 weeks ago for a perforated small bowel and got a temporary ileostomy that's high up in the small intestine. It's so active that I have to be on IV fluids at home until I have it reversed next month.
When it comes to getting a tight seal with the wafer, I cut the hole in the wafer off to one side to shift it away from the belly button. Hopefully, that will work for you, too.
Dx'd Crohn's in '99 at 28. Proctocolectomy and ileostomy in '06.
Disease-free, medicine-free, and very thankful to be healthy again.