One big consideration is if there are any windows high up on your existing walls and if the new floor will mesh with the level of existing windows.
Do you need the new area to be completely enclosed or would you consider a half wall which may limit the need for any additional ductwork, also depending on how hot/cold that side of the house gets.
Your style of floor plan usually has flood lights or some type of lighting up high, wiring may not be a big deal, it depends on what you plan on having in your new area other than lighting. Existing breaker may be fine.
Insulation is typically only in attic, adding floor space shouldn’t have any affect.
