The couple that I've hand pieced, I pressed to the side because that was the 'correct' way. Used to do that with machine piecing as well but now I press virtually all of my seams open. I find it makes my points cleaner due to less bulk. When hand quilting the machine-pieced, open-pressed seams, stitching in the ditch is WAY easier. I've migrated over the last few years to more 'echo' quilting about 1/4" away from seams - easier still and this way my quilting actually shows! If you're hand quilting less than 1/4" away from the seams, I don't know that it would make much difference which way you pressed. That one additional thin layer of fabric won't make a huge difference in ease of quilting or lack thereof, in my opinion. And I think as long as your stitches/inch are reasonable in your piecing I would think they would hold up just fine. Look at the number of antique quilts out there that are hand pieced and hand quilted!