I have a stoma, or ileostomy bag fitted on my abdomen due to crohns disease.

When I perform ghusl I obviously remove the bag in order that I may be able to access all areas of my body/skin for the sake of purification but there are times when I would experience feacal discharge whilst performing ghusl, does this nullify my ghusl and would I have to restart? or can I continue and do wudhu after instead?

If the discharge reaches or touches a part of my body whilst performing ghusl, is it enough that I run water over it & wash it away and continue with my ghusl or do I need to re do my ghusl all over again?

If you are not able to hold feaces at all, even until the ghusl is completed, then your ghusl is valid, and you do not need to repeat it, and your prayer is also valid.
Yes, you need to purify the impure place and the impure hand.
I ask God Almighty to heal you