I felt the same way when I first started. Most quilters in my sewing group insist that you should only use cotton thread for cotton quilts. I have been using poly thread but you do have to be careful and wind slowly on your bobbin because it stretches and will leave puckers. To pick colors, i lay several possibilities out on my fabric to see how it blends. I even sew with different ones on my scrap pieces to see the result.