soffit vent question

Before you add or change anything do plenty of research on attic ventilation. There is a slue of it available for anyone interested.

This will get you started on some basics.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attic-venting

https://www.homeadvisor.com/article.show.5-Myths-about-Attic-Ventilation.16547.html

going by recommended NFVA calculations of 1 sq ft per 150 sq ft of attic footage it would require 8 sq ft total of NFVA for your 1200 sq ft house. Fifty % coming from exhaust vents or ridge and fifty % intake or soffit. Of the 50% coming from the soffit that should be split between each side and continous from end to end.
So ideally you would be looking at 2 sq ft or 288 sq inches of NFVA of vented soffit per side.

But even with all that said, are you seeing any signs of needing more ventilation.
Shingles curling from cooking in the summer?
Condensation in the attic? Mold?