Wow! Great quilt and lots of work with all of those squares! I'd start with a narrow brown border the size of the squares, so 2". Not sure what beyond that. Ok, just did some Pinterest searching...what about a wide brown border with a row of red and tan blocks like this one:
https://www.pinterest.com/pin/210543351305029817/ Actually, I think I'd like it best just using the reds, to keep the border darker to frame the quilt.