When building a barrel wood stove you should line the bottom and part of the sides of it with some firebrick to help prevent burn through of the barrel.
If you use firebrick you shouldn't need a grate unless you really want to. A grate would just make it harder to clean the ashes out and harder to get a good amount of wood in it.
I have a barrel stove and I just use firebrick and it has worked fine for years now.