Nice grow! I realize that you've already covered most of this but thought I'd chime in since I've recently had some of the same questions come up in my grow.
I'm growing in RW slabs and like them alot - but would make certain to flush them well before growing in them again (moving to aero for next round) I dealt with ph creep - roughly 1 point a day, for about the first month because I failed to flush before starting, it gets old testing and adjusting 2x / day - fortunately that part is over now.
I also use 29% H2O2 - at a rate of 3ml/ gal - granted, I'm new to H2O2 (and this is only my second grow), but this concentration helped get rid of fungus gnats with no ill effects on the plants, so...
Last - I did not realize it with my first application of H2O2, but apparently it will destroy organic nutes. Since I'm using Botanicare Pro Grow/ Bloom this was an issue for me. Now I only use peroxide during flushes with PH'd water.
I'm currently growing White Widow too - it's a hearty, dank smelling little plant and it appears that the yield is going to be much better than my first round of bagseed.
Good luck.