If it helps, I'm brewing my first Fruit Lambic this weekend...
I made a yeast/bacteria starter from
Lindeman's Gueuze Cuvée René which, despite what people in this thread are saying,
IS a true lambic. You will develop quite a "pucker face" drinking this dry, sour gueuze.
I made the starter with DME, sugar, and maltodextrin (something for the bacteria to consume) and let it go for 4 weeks. I've been tasting it weekly and it's becoming quite sour now. It already has the horsey, tart characteristics of a true lambic in less than 4 weeks. So, the original yeast and bacteria are very much alive and ready to due their worst.
The recipe I'm using is all grain - 70% 2 row, 20% wheat, 10% honey malt. The honey malt will provide for some unfermentable, complex-chain sugars for the bacteria to consume after the yeast have done their job.
I plan to pitch the bacteria starter when I pitch the yeast (US-05). The yeast will produce alcohol very quickly, so I have no fear of uncontrolled bacteria growth. After primary fermentation is complete, I plan to rack to secondary on ~3lbs of raspberries and a few ounces of oak chips (provides a lattice for bacterial growth).
I plan to sample it bi-weekly and rack when I'm satisfied with the overall flavor. This may take 4 - 12 months but, based on the speed of the starter, I suspect I can accomplish a good, true lambic flavor in less than 6 months.