For your question, besides the difference you've mentioned in terms of the construction of sentences, in terms of meaning, there is a slight difference between the two: the former one can be understood as "I am energetic." the later one can be translated into "I tend to be energetic". "-편이다" emphasizes "a tendency" hereby. So, "rather" is not suitable for the THIS case. e.g 나는 보수적인 편이다. I tend to be conservative. This implies that " Yes, I am slightly conservative, but I am not that so(rather) conservative." Hope this makes sense to you. : )

Yes. Both of expression basically mean a same thing. But I think "noun+인 편이다" is a more euphemistic expression.

Hi Kate, I want to learn russian.