Hello Christine.
I am not sure what the challenges are with regard to fibre. As I understand it, there is lots of fibre in fresh fruit and vegetables If not, then there are supplements like Fibogel, Metamucil and many more. These often come in powdered form to be mixed with liquid. I know this because it is what is recommended for older people when they become less active and are more likely to become constipated.
I have quite a number of years experience as a vegan, but don't feel I have very much to offer in the way of tips. I have simply eaten anything and everything that I like which doesn't involve killing or abusing animals in any way. Now, If it came to eating humans, then I might have to rethink my stance on veganism (just a joke) !
For me, the challenges come more in the way of keeping a balance of the various vitamins that may or may not be sufficient in a vegan diet. I 'manage' this by popping a few one-a-day pills of one sort or another. However, it is as well to keep an eye on any contra-indicators in this regard if you are taking prescribed medication or have medical conditions that might be affected adversely by plant-based supplements.
When I looked into it, I found that turmeric was one of those substances that I should be staying well clear of, but my wife has absolutely no problems with it.
If in doubt, I would suggest that you 'Google' whatever you're taking and add 'contra-indications'. This will give you a more precise understanding of what the 'experts' have to say about these things.
There are also quite a few vegan recipe books appearing on the market, which can be quite enlightening for those who are just starting out on this vegan journey. As for having a stoma, I doubt whether being a vegan makes much difference but, as many have pointed out before on this site, it tends to be a matter of try it (whatever 'it' is) and see how you get on, as we are all different in the way we digest food, so what is okay for one person, may not be so for another.
Best wishes
Bill.