I think because they would most likely be new I think the character should grow into the full strength over time. So start at 2 or 2.5 and slowly go to 5. Really it is up to you, as long as you do something to show their is growth it should not be a problem. I have given my character some limits at the moment though they are not very good ones due to the powers she has, she more of a modified mutant like Wolverine barring the nose thing.