Oven spring and crumb troubleshooting advice?

Hi! I've been baking for several years, but recently moved to a new apartment and struggling with variables.  In general my bread always tastes good and has a good crust, it's the crumb and oven spring I'm struggling with.  I've been trying to follow the idea of "watch the dough, not the clock," but I feel like I'm getting mixed messages between all the "tests." I have some suspicions about a combination of factors, but could use some advice about which ones are the most likely causing issues! This is long because I'm trying to give detail, but a summary of my suspicions is at the bottom.  

I made a basic white loaf to test out some suspected issues, and followed the basic recipe as given: all white bread flour, levain 15% of flour weight, 80% hydration, 2% salt.  

Problem 1: I keep seeing that it takes several hours for starter to double in volume, and mine doubles sometimes in a single hour. Room temp is not unusually hot. It has never passed the float test, but I've also read that the float test isn't always 100% accurate, especially for non white grains (and here I confess that I feed mine 25% rye). My starter is kept at room temp, fed once a day at 100% hydration, survives being starved for a week at room temp or weeks in the fridge, and always smells like sticking your head in a bucket of ripe apples. It's indestructible.  

After confirming it failed the float test a few hours after feeding, though at what would appear to be its "peak," I built a levain with it using 1 part starter to 2 parts flour and 2 parts water.  It doubled in an hour and passed the float test.  

I had autolysed the flour and water for about 45 minutes and then added the levain and salt.  I left it at room temp for 6 hours, stretching and folding every hour for the first 3 hours. 

At that point it looked and felt great, exactly like all the professional high hydration dough videos I've watched (80% is high for me). I divided it in two mini dough balls and preshaped them, let them rest, then shape them and put them in flour lined ceramic bowls, covered in plastic, in the fridge overnight. 

Potential problem 2: the dough didn't noticeably rise, just got really extensible, soft and noticeably fluffed, but not anything I'd call rising, really.  

8 hours later, nothing has happened.  Dough is super cold and stiff, fails the poke test, but there are large bubbles under the surface. I take them both out onto the counter for 2 hours.  After that, a poke test looks OVERPROOFED! Visible bubbles, dough is soupy.  Loaf 1 I pour into the hot Dutch oven and it's a pancake.  Loaf 2 I reshape, rig up a makeshift couche so it doesn't turn into a puddle again and leave on the counter while baking loaf 1. 

Both mini loaves baked 15 mins with lid on at 250C, 15 mins with lid off at 230C. 

Results: 

Loaf 1: basically ciabatta. I'm happy with the crumb but not the shape.  It lost 21% of mass during baking.  

Loaf 2: incredible oven spring, even too much.  Crumb has large holes and dense areas, crust is soft and chewy but not bad. It lost 14.5% of mass in baking. 

Neither appear overproofed to me (maybe I'm wrong?), although the dough felt badly overproofed. 

In the past, my best loaves have been bulked in the fridge, shaped and then left for an hour or so before baking, but why does this work and how can I get it proofed enough without over proofing or losing shape? I like the idea of the final proof happening in the fridge because of the oven spring from colder dough, the scheduling convenience, cold dough being easier to handle, and the idea that I'm trying to handle the dough less at later proofing stages, but I'm not sure it's really working.  

Suspected issues: 

1. I should use my starter sooner after feeding (and why is it so extremely fast?) 

2. ambient temp is too cold for the first several hours of proofing time

3. I should use more or less levain in the build? A super active starter suggests to me that I should use less, but the final crumbs tend to look underproofed, so.... 

4. longer bulk time in room temp?

5. fridge is too cold (4C): forget the fridge entirely, or proof it most of the way at room temp after shaping before fridge? 

6. more time at room temp after fridge and before baking? 

7. shape after fridge instead of before? 

8. less hydration in initial build? 

9. just practice handling high hydration dough more? I'm fairly OK with my shaping techniques (for my purposes at least)--it's what happens to the dough after shaping that's bothering me. 

Any ideas on where to start troubleshooting would be great! I feel like I'm missing something obvious right in front of my face!