Having lived in Georgia, Alabama, or Florida for the past 13 years I am a big fan of the Columbia fishing style shirts for hot weather activity including fishing and backpacking. The quick drying materials, the venting. The button front, cuffs and collar serve more than an aesthetic purpose. When it is really hot I walk with my collar up to protect the back of the neck, chest open maybe 2 buttons down, bottom not buttoned all the way so that the shirt opens not enough to see my stomach but enough to catch any breeze or airflow there is, sleeves down when sunny, cuffs unbuttoned. All combined you set yourself up to catch a lot of air/breeze this way through the cuffs, button holes, bottom of the shirt, and chest area. If it cools down all of this can be reversed. Also at night we will unbutton the shirts and lay them out to dry, sometimes inside the tent. (BTW I don't actually wear Columbia, I buy knock off brands similar in design).
I understand your logic with the hood and thumb holes but I don't think it is going to work, especially in the southeast.
Combine that with this hat or something like it if it is sunny http://www.columbia.com/Omni-Shade%E2%84%A2-Bora-Bora%E2%84%A2-Booney/CU9745,default,pd.html .