Tons of people piece their quilt backs. Alot of the pieced backs look awesome. A straight seam is what is needed to hold things together. Nothing else needed as far as sewing seams together. As far as pressing seams, I used to press open but then the seams are not as strong. I would press the first column of seams upward and then the next downward and continue alternating until you do every column. Then you can "nest" the seams next to each other to make sure they line up perfectly when you sew them together. (hope that makes sense). This will make your seams line up across the rows. My biggest suggestion is to consider a long arm quilter (LAQ) to quilt the quilt. B/c of the the weight of the quilt, the book I have on t-shirt quilts strongly recommends using a LAQ to quilt. Hope this information helps.