The Perfect Loaf Weekday Sourdough

I'm a new user and I'm very excited to join this community! I'm super impressed with the supportive and positive atmosphere that has been created. I've been a sourdough baker for years but haven't really been consistent in my methods until I recently read a blog post about starter acidity and its effect on gluten which got my brain buzzing. It prompted more reading which brought me to TFL a few weeks ago. Since then I've chosen my practice loaf, actually started taking notes,  and have been happily nerding out on it. The following are my notes from my second bake of the Weekday Sourdough from Maurizio Leo's The Perfect Loaf.

https://www.theperfectloaf.com/simple-weekday-sourdough-bread/

This was my second bake of this recipe-notes from the first one didn't have photos. I was also running a side observation aimed at improving my reading of starter maturity and inspired by the usage of aliquot jars that I had read about here on TFL. Those notes are in parentheses.

2/6 ~ am- fed mother starter

2/7 4 am- removed portion of starter tor levain build, fed ~40g flour 40 g water
8 am- levain nearly double, fed 80g flour, 80 g water
1:30 pm-levain doubled, bubbly and crowned on top, mixed autolyse:
700 g white, 225 g ww, 176 g levain, 639g water
(Put some of remaining levain in shot glass to gauge further development, filled to 40ml line)
3:30-went for a ski hence autolyse ran longer than called for, dough well hydrated and starting to rise
Added 19g salt and 50g water, dough hydrated but still shaggy, breakable strands
(Levain in shot glass at 65ml line, conclude that it was still actively growing when mixed into the dough)
4:05-4 coil folds, dough smooth and holding air pockets
4:35-4 coil folds, nice elasticity, more bubbles, not super extensible
(5:00-reserved levain at 85ml line)
(5:30-reserved levain at 90ml line)
(6:00-reserved levain still~90ml, conclude it has stopped expansion, built new mother from it using 1:1:1 ratio as previous mother had developed too much acidity. Previous mother will be waffles in the morning )
6:30-dough is starting to have a bit of jiggle, small bubbles well distributed over the surface
7:00 removed dough from the bowl w/wet hands, divided it into two and preshaped each piece into a round and left uncovered on dry counter
7:30- w/floured hands on a lightly floured counter flipped each round over and letter folded into a boule, transferred to well-floured dough baskets and set flat plastic bag on top, set on middle shelf of fridge which tested earlier at 39 degrees.

2/8-4:30 am- preheated oven and vessels @475 degrees,
removed loaves from fridge, slightly crowned and look alive

4:50-turned out loaves onto greased foil and slashed, cold dough made it far less frantic. Lowered loaves into vessels using foil, ripped off excess foil, covered and loaded into oven, reduced temp to 450. Baked covered for 20 minutes. Removed covers, loaves well-risen and DO loaf has a bit of crust peeling back around the top slash! Baked uncovered 20 min @450, then reduced temp to 365 to discourage overbrowning. Baked 18 minutes more. Evacced from oven and removed to a cooling rack, all looked lovely until inverted and found the bottom crusts had burned!
Not sure of the culprit, maybe don't set DOs directly on the stone? Or did it have to do with the foil...? Will try with vessels one rack up next time, also maybe try with stone on upper rack of oven?

Signs of underfermentation in the crumb though it was soft and well baked, no gumminess. Crust was disappointing, lower crust was understandably hard to slice but even the top crust was harsh and clawed up the roof of my mouth. Flavor is nice and fresh but not very interesting.
Goals:
1. Better, more developed flavor-hope to achieve through higher ww content, mix-ins and longer cold proof. Also more mature levain could help?if 2. Light crisp crust rather than harsh and scratchy- hope to achieve through???...maybe higher hydration?
3. More even size and distribution of holes- hope to achieve through longer bulk ferment with more folds

I'm interested in any feedback folks have, I'm at this moment on my third bake of this recipe at the beginning of bulk ferment. 

Many thanks!

Arwen