First True Sourdough Loaf

My patience with creating my starter has paid off, I finally decided the little guy was vigorous enough to be forced into labor.  I put together a small loaf so that I could do a test run, and get some confidence that my cultured yeast could do the job.  First, the money shots......

Ok, I have to say, I'm pretty darn pleased.  My scoring turned out better, I love the color on the loaf, and am very happy with the crumb texture, flavor, etc.  I honestly didn't detect a ton of sourness, but I can play with amount of starter, ferment times, etc. for that variable.  I think I would back off on the whole wheat just a bit for the next go 'round.

A bit of a confession.....the first photo is showing my loaf from its best side.  I did get some "blowout" at the very bottom of the sides.  What causes this?  I'm thinking underproofed or overworked.  Maybe a bit of both?  Here are the particulars:

120 g whole wheat starter (100% hydration)

145 g H2O

225 g Bread flour (King Arthur)

15 g Whole wheat flour (also King Arthur)

8 g salt

My math says this is 68.3% hydration.  I mixed all to combine (starter and water first), forgetting to leave the salt out for a 10 minute rest.  After the rest, I kneaded briefly every 10-15 minutes for 90 minutes, then let it bulk ferment on the counter for another hour with 3 sets of stretch/fold.  At that point, I was trying to accomodate my schedule, so the whole shooting match went into the fridge for a bit of retarded fermentation.  After 16 hours in the fridge, the dough had not risen noticeably at all, so out it came for about 3 hours still in bulk.  At that point, it appeared to have not quite doubled (defininte signs of fermentation), so I shaped it, and let it rest inverted on a tea towel in my plastic colander.  After two hours, I turned it out onto my pizza peel, and scooted it onto my stone in a 500 degree oven.  I added about a cup of water to an empty pan beneath the stone for some steam.  After 20 minutes, I had nice spring and some great color forming, so I took out the water tray (dry at this point), and turned the oven down to 400 degrees.  I let the loaf cook for another 25 minutes when temp measured about 210 (so said my Thermapen), and it sounded hollow.  Out it came to rest, and the remainder you see.

I would welcome any and all comments based on my text and photos.  I feel like I had a pretty good command of the timing, though the blowout suggests that I may have not proofed long enough.  No comment is off limits, I want to bake the best bread that I can.  This one was really good (one of my best so far), and I'm eager to turn it up as many notches as I can.

Thanks for looking!

Rich