You can but you won't like the result. Vinegar is acidic whereas sherry is a sweetner, flavorer after the alcohol cooks away.
In most recipes, sherry would be appropriate. Often sherry vinegar is used in place of sherry by those who want to avoid alcohol. The exception might be when preparing a salad where the greater...
raspberry vinegar, red wine vinegar
Sherry wine will make it much sweeter.
No
U can use an observorant cloth sherry recipe it is excellent