1- The cast, splint or bandage must not transcend the place that needs care and the necessary portions surrounding it.
2- It is not a condition that one should be in a state of purity before putting them on, neither is there a prescribed time limit for wiping over them. As long as there is a need for them to be worn, it is permissible to wipe over them even when removing the greater state of ritual impurity. But when the need for their use ceases, they must be removed and henceforth the parts underneath must be washed during
al-wudu’ and bathing.
3- As for band-aids and bandages etc
source:
https://www.al-feqh.com/en