You've gotten great advice that I can't add to already on the Y seams. As to general accurate machine piecing, I suggest starching as well and slow down. Some really finicky blocks are better just done with paper piecing. General piecing, however, certainly aim for that perfect 'scant' 1/4" but more importantly (to me) is being consistent with your seam allowance.
As to starch, I use the liquid Sta-Flo brand and mix to a 50/50 solution with water. Let the starch (regardless of type you use) to soak into the fabric a bit before pressing/ironing. A - it makes the fabric stiffer and B - you don't get flakes.
Good luck with your challenges.