Here's my speculation... though bread forensics are not worth much if
you cannot attend the autopsy.

The sourness issue... I think you fermented the starter too long the
first time around. You were able to transfer a good acid load to dough
#1 since it was a new (and balanced) starter. But the starter returned
to storage was overly acidic and it could not propagate LB's in the
numbers you needed. This was compounded by using a large amount of this
starter for bread #2. A smaller amount would have been effectively
de-acidified by the larger volume of fresh water and flour.

The remedy is to keep 2-3 tablespoons of starter. The volume build-up
from a much smaller starter inoculation solves the acid issue will
actually make for more sour at the end. It's counter-intuitive, I know.

The crust... The flyaway crust you experienced in bread #1 was caused
by two things. An insufficient shaping technique that did not properly
deflate and align the dough's gluten and too long a period between
shaping and baking. You correctly identified half the issue. But
appropriate rounding and shaping are key for distributing gas and a
developing a tight outer skin. It's the skin tightness that keeps the
bread from slumping and spreading. Rounding and shaping are hard to do
correctly. It takes time to get the hang of it.

Remedy: get a book with pictures that shows the process. Look into
Peter Reinhart's books. They have more pictures and illustrations than
most.

The crumb... machine kneading does not make the best crumb. The gluten
is shorter and not as extensible. Others will swear by their
KitchenAids and Swedish what-chu-ma-call-ems... but not kneading is
best. Use the machine to mix the ingredients, then let the dough rest
in a cool place like a cellar or refrigerator for about 12 hours.
Longer is fine. Gluten forms with water and time. It's a hydration
process. Kneading or time both distribute water. Time is better. This
cold rest is called a retard. It is not a proof. You still must proof.
But you can skip all of the various punch downs. They serve no purpose
in sourdough. They are a relic of yeast bread instruction since yeast
breads get very gassy.

The taste... There is no thing as a "short" cooling. Tempting as it is,
the bread must cool to room temperature and should be at room
temperature for at least 3 or 4 hours. If you want warm bread, reheat
it. The really interesting flavors do not present themselves until the
bread is well rested after baking. This is another one that is counter
intuitive and very hard to practice, because warm bread smells so
wonderful, but it's true.

Perhaps someone else can do the oven temperature, time and stone <g>...

Good luck. Keep posting.

Will