Sometimes on a block with many pieces like yours, it can help to draw a map of the pressing directions. Draw the block and put a little arrow on each seam. Keep that on your ironing board and you'll soon be nesting without even thinking about it.
I pin both sides of the seam allowance and remove the pins just before the needle gets to them. The top seam allowance should point towards the needle so it pushes towards the seam when you sew and not away from it.
I never press my seams open and the blocks are still dead flat. No matter which way you do it, there are still two layers of seam allowance and two folded seams on each side of the seam line so the only difference is in how sharply you press.