1) Can you go into this in more detail? I'm hard up for some homebrewed sours right now and I don't now if I can wait until the 20 gallons in planning age out.
I'm obviously biased and think my* technique is good, so I took a bottle to the brewclub meeting last night. The people who liked sours liked it, and they were all surprised it was only 4 months old.
In a nutshell (20L batch, 1.050-1.060):
1) prepare a 2-3L sour starter with 100g/L of dextrose, 1/2-1 cup of base grain, and keep in the 100-110* range for 2-3 days before brewday.
2) On brew day, mash as usual for a target of 17-18L finished wort.
option a. Mash and boil 100% of the wort as usual
option b. Mash as usual, reserve 7-8L unboiled wort, boil the balance as usual to end up with ~ 10L of boiled wort.
3) If you did option a., separate the boiled wort into 10L and 7-8L, add B. lambicus and BM45 (or wine yeast of your choice) to 10L, add sour starter to the remaining 7-8L. If you did option b. add the Brett and wine yeast to the boiled portion, add the sour starter to the unboiled portion.
4) Ferment the 10L non-sour portion as usual. If you want to start layering oak flavor, add about 15g~1/2oz oak of your choice.
5) Keep the 10L sour portion hot (100-110*) until it's fully soured. If you have a pH meter, mine usually bottoms out around 2.3-2.6 within 2-4 days. Once it's dropped into the 2's you don't need to keep it hot anymore.
6) Once the non-sour portion is in the double-digits (a month or so), you can blend the portions to taste. You have to use a little bit of imagination, because it'll taste a more sour when it's carbonated, and it'll taste more sour when it hits terminal gravity, but it's not a huge difference. Just err a little on the less-sour side. You can check pH of the blended beer too. I like 3.5-3.6, if you want more sour you can just increase the % of the sour wort in the blend. Don't be afraid to waste some wort if a 60/40 blend tastes better than a 50/50 blend.
7) Oak your blended beer as usual (maybe another 1-2oz, depending on how oaky you want it).
#8 Once gravity has bottomed out, prime with fresh yeast and bottle in a heavy bottle. If you want to get fancy, you can use Kai's priming calculator based on where you think the Brett may drop the gravity over a long period, and take that into consideration. But if you use a Champagne/Belgian bottle rated to 5 vol and carb to 4 vol, you'll most likely be fine.
OK, so that's really complicated and a lot of work. Why bother? With this technique you can lock in the sourness where you want it. In my experience, the grain-cultured Lacto won't further drop the pH if put into an alcoholic environment with little sugar left to eat. It may form a pellicle again in the blended beer, but from my measurements pH remains stable. You'll need to pull samples to taste every couple weeks. Let your tastebuds guide the process and timing.
What I've done most recently is keep a bucket full (18-20L) of sour wort at all times, and taking off portions as I need it, topping up with excess wort from whatever batch I'm brewing. If you build up a large enough colony of Lacto in the bucket, you won't need to keep it hot, or mess with making a sour starter before each batch.
*This technique is an amalgam of other people's techniques, notably the "fast lacto and brett" thread on HBT, and Mike's (the mad fermentationist) blog. And people have been using fractional blending for a long time, so I'm not trying to take an undue amount of credit.