I had my gallbladder out way before my j-pouch surgery and I've never had any problems. I think you'll find (hopefully) that you'll do very well with it gone.
Did your bowel movements increased? Permanently? No way to tell.
Have you had more irritation? Same, no way to tell.
Have you had more dehydration? I never get dehydrated.
have you experienced any vitamin deficiencies (such as A,D,E,K)? I had a Vitamin deficiency but I think many people do, whether or not they have a gallbladder and a colon. No other deficiencies.
Did you gallbladder pain go away? Yes! Absolutely! And that pain was horrid!
Has your diet changed? Nope. I'm a lacto-ovo vegetarian and I eat whatever I want.
Are GB problems common for J-Pouchers? I'm not sure. Mine happened before j-pouch surgery so I have no idea if there's a link or not. Others have had surgery after j-pouch.