Certainly happy to hear that you are tackling this intersting regiment.
I am doing one on Georgia's Civil War flags and have a number of files on the company flags of this regiment, several of whcih were lost in the Rich-Cheat Mountain Campaign of 1861. The GA Capitol Museum has one flag from this and possibly a second. One of the GA unit flags, Southern Guard Co. D, made it to the US War Department and was depicted in a March, 1862 newspaper but has since disappeared. Atlanta History Center has another flag of the regiment - Gate City Guards - but it is the replacement flag for the one lost at Rich Mountain.
The GA State Archives has a lot of information on this regiment on microfilm in the CW Miscellany section that is worht going through. The period newspapers of Georgia, particularly those of Atlanta, ran a number of reports, articles and soldier letters from the regiment. I have seen a huge number of them in my newspaper research.
Additionally, for this campaign, you should hit Ohio and Indiana newspapers for the Rich-Cheat Mountain Campaign as there are details in those that will be very helpful.
Lastly, Keith Bohannon and Mike Purdy are two of the greatest epxerts on GA units and they are both worth getting in touch with for other soruces for the unit. I have emails for both men if you need them.
Please let me know what you might have uncovered for their regimental and company flags - I am happy to exchange information.