If you are worried about absorption of vitamins, I would ask your doctor to run a complete checkup on you to see if you are deficient in anything. This is more of a concern if it is small bowel disease you had as that is where nutrients are absorbed. With large bowel disease, dehydration is the main concern, and with perianal disease or fistulas it can affect birth. And as you have had bowel surgery, you will need to find out how that will affect the birth too.
If you're not taking any maintenance meds then I guess you need to have a plan in place just in case you do have a flare up while you are pregnant. Better to research the options now so if anything does happen you can get on top of it quickly without it affecting baby.
In the UK, midwives and doctors don't routinely weigh patients because sometimes people get too hung up on how much they weigh, and mother's weight gain doesn't necessarily correlate with baby's. But I found it reassuring to weigh myself every couple of months or so, and to measure my waist in the early weeks before I got a proper bump- I figure if I'm putting weight on then I must be absorbing OK and if my belly's growing then baby must be.
I don't think there are any specific questions you need to ask, but keep a pad and pen handy so if anything crops up you can make a note of it and remember ask your docs.
Oh, and just to warn you- you may need to play around with your Immodium dose, I found I was much looser in the early weeks but now I'm tending towards constipation, this is common in the last 1/3 of pregnancy as hormones slow your bowels and baby bouncing around in there doesn't help!
Good luck, and keep us updated as to how you're getting on