To cut all first or not???

IBeing new to the cutting of squares and tri's etc...I started cutting all out at one time. However.with so many mistakes and mis cut squares and such...I have discovered 2 things that help me alot.
1. cut pieces a scant more than what you need...about 1/8 inch. If you want a 2" square, and are supposed to cut it 2,1/2" to allow for 1/4" seam allowance on each side. I did this and they never came out matching..always to short, crooked etc. So I tried it with the scant 1/8" inch...and it worked out perfectly. I am working with them now and everything is sewing together just right.
2. While on this project, since I am working with strips and rows....I am doing one "thing" at a time. My kitchen table is the other side of the house from my sewing room, but I need the exercise! So I measure and cut the strips that go around the middle square, go sew/press them. Go back out to the table, and measure and cut the next set of strips, go sew/press. It sounds like alot of movement, but like I said...good way to get exercise and not so weighed down at the machine.
I do see that maybe with the squares assembly this might not work...so I would cut enough squares for 2-3 at a time. That way, if I have made a mistake, ALL my fabric isn't used up! I learned this on a quilt I have the top done, but need to starte layering it...I cut squares out for the whole quilt, and then sewed them up and the blocks didn't match..some bigger some smaller. So I had to cut out the WHOLE set of squares AGAIN...and this time...they were all TO SMALL!! So I had to cut them out AGAIN....and well...I finallly ran out of fabaric and had to adjust them..and my once wanted 12" blocks are now 8" blocks! So, if I had done 203 blocks at a time, I would have found this out LONG TIME AGO!!!