Aww, man! You're going to make me do some serious evaluation!
No problem, though.
I'd switch the black malt in the recipe for carafa III. Mike Tonsmeire is a great resource, but I find the toasty notes in black malt and roasted barley to get acrid in a sour beer.
Process is sound. I would add the oak right after primary fermentation. Smaller amount, boil the cubes a couple times to extract the harsher compounds. But let the brett go to work on it.
As far as bugs for primary versus clean yeast and bugs in secondary, it depends on whether you want to keep bacteria out of your primary fermentors. If you use buckets for primary, and don't want to dedicate it for sours, ferment it out with a clean yeast and add your bug blend in secondary. But the blends are really meant for a primary pitch.
I like to use the blends for primary and pitch it all in a carboy. Either use a 6.5 gallon carboy and make a 5 gallon batch, or make 4 gallons in a 5 gallon carboy. After it settles down, top it up with some wort of a similar gravity and leave it in primary for as long as it takes.
I think 5# blackberries in 5 gallons of sour stout is going to disappear. I'd double or triple it, or check into wine bases.
And check out Mr. Tonsmeire's book, American Sour Beers. Some of the info is out of date, but it's a great starting point.