Almost all recipes are calibrated for 70%, which I think is probably considered average. Some people get 60% and buy more grains, some get 80% and buy less. Really what I did was aim for simplicity in my process, did a couple of recipes and found out I got 80 and was happy. haven't really read about anyone getting over 85 though... 90 and up pretty much gets a universal reaction of "you measured something wrong" haha.
I squeeze my bag pretty well and no sign of bad flavors yet. I don't go crazy though, I just twist the bag until the grains are in a solid mass and push on it with my spoon. I do it twice, one lightly when the main mash is done, pretty much just to get enough liquid out to not spill all over the place when I go to sparge. I do a batch sparge by putting the hot water in one of my buckets and then dropping in the grain bag, sticking my spoon in the bag, and giving it a good stir, then wring it out a bit harder after 10min.
Did you taste it? My first all-grain was a BIAB oatmeal stout and I was pretty happy with myself haha. I had done an extract oatmeal stout and the all-grain knocked its socks off flavor wise.