...when you say 1 cup of Slippery Elm, you should be meaning 1 cup of Slippery Elm porridge/gruel, not 1 cup of Slippery Elm powder.
A tablespoon or two of aloe gel in a cup of porridge is good. There's no set rule as to how much. In fact, some folks choose to have their aloe gel separately (or mix it in juice), and that's fine, too.