I had my total colectomy 57 years ago. You should have no limitations
You will be able to swim as much as you desire. There are no restrictions.
Some foods you eat take longer to digest. For example, when I eat my bowl of oatmeal with blueberries, apples, almond butter and sesame seeds in it every day, which has a lot of fiber, it will take 3-4 hours to digest through my system. You just have to experiment what foods work their way through your system more than others. Additionally, one has a large amount of small intestines, so its not like what you consume goes through your system immediately.

Vitamin D is absorbed in the SMALL intestines, as are the majority of nutrients. In fact, the main function of the LARGE intestines is to absorb water and electrolytes. The only vitamin you may need to supplement via a monthly injection (and you can give this to yourself at home) is B-12, as B12 is absorbed in the ilium, which you may have removed with an ileostomy.

I cannot stress enough the importance of staying hydrated. I learned the hard way. When I was working, I was drinking too much coffee and not enough water and that caught up with me over 55 ;years when my kidneys failed due to chronic mild dehydration. I was lucky enough to get a kidney transplant 1.5 years ago. So, drink more than the amount required of a person who has not undergone this surgery. I drink 2.5 -3 liters per day with electrolytes in it. With an ileostomy you lose a lot of your body's electrolytes.