Do first decan have the sun signs typical traits more predominately?

Actually the first decan of Aries is Aries Decan so this would strengthen the Aries Energy of your Sun.

Decans have a very mild effect upon the energy of our planets though it can explain a little more detail about that planet.

For example, I have Aquarius Sun Second Decan Gemini which heightens the talkative nature of my Aquarius Sun. Mild, but interesting to know.

Hope this is helpful and good luck and bless you too.