I'm not vegan, but I do follow a mainly vegetarian diet (I still occasionally eat fish, but otherwise no meat). Although we do have a couple of other vegans on this forum who do very well, in the early stages post takedown, you may have to make some concessions with what you eat, meaning that unfortunately, you may not be able to follow a strictly vegan diet (if even only temporarily). Given your digestion issues as you describe them, you would probably have to start back with a very bland diet and give your system some time to adjust, and then gradually add back the foods you were accustomed to eating before, a few at a time, and see how you do with them. Obviously low iron is a problem for you; I struggled with it for years after my colon was removed. It's really only been in the last 2.5 or so years that my iron levels have been stable, so I understand how you feel. If you are not taking an iron supplement, you should be. If your levels are very low, infusions may be a suggestion. Also, considering that you have followed a vegan diet and also have IBD, you should get your B12 levels tested as this may be an issue for you as well. Your overall protein levels should also be evaluated.
At this point, you should be looking to blander, bulking foods such as rice, oatmeal, toast, bananas, and peanut butter as good options for calming your digestion and easing up on the "butt burn." The bleeding you are experiencing could be cuffitis or pouchitis, but it may also be plain old run of the mill hemorrhoids or irritation, and a blander diet should go a way toward easing that. If you can make an allowance for Greek or Icelandic yogurt, this is a good choice as well. As far as eating vegetables at this stage, blended soups are something I have always been able to manage. Juicing is good option too, but make sure you watch the sugar content of the fruit, as excess sugar is a culprit for poor pouch function for many of us.
Hopefully in the future you will be able to get back to eating the foods you are used to, but in the meantime, you may have to make some modifications to your diet, at least until your system adjusts and normalizes.