Making the devour and fire mutually exclusive is a deliberate choice so that players can't just constantly devour while firing, making a window of vulnerability. As far as the weapon swapping goes I'm not sure if that's the case I'll check out what I can do for that, I don't recall keeping any checks for making that exclusive from other inputs. Tool-tips will be there, as I said there will be tutorials in the story mode and every time you unlock a weapon by beating a boss in one of the levels you'll get some kind of tutorial explaining the weapon's mechanics.