It might work. I know those are superb for hermit crabs, but I've never heard of someone using it with a bowl. Should be alright since it's not in the tank itself. Anything under 2.5 gallons shouldn't have a heater in it. Is the room you're keeping the bowl in a constant warm temp? If so, you don't need a heater at all. I don't use heaters for any of my betta tanks.
Can't help you with wattage, sorry.