It;s a good question, your instructor should cover all of this. You can also go to the UK CAA Safety Sense leaflet on icing in piston engines. There's another one on winter flying.
Safety Sense Leaflet 14: Piston Engine Icing | Publications | CAA
You can assume 10% less power, but a 44 with just you in it isn't going to be an issue. Also, you're going to be 10% down on cold air performance, which is pretty dense, and better than 80 degree air + carb heat.
As you are reducing the power, you're going to burn more fuel, you could knock off 10%, but again, you instructor should give you guidelines.
You can pull carb heat as much as you need to stay out of the yellow zone. However if the instructors approve, you may have it out full for the whole journey, depends on their procedures. Not great for the engine if done often.
Just remember that if you do get roughness/odd yaws etc., and your carb heat isn't full out, pull it and keep it out for at least 30 seconds. Things will get worse before they get better as ice melts and water hits the cylinders.
... or migrate to a raven II....
Lafite