Flanders' Reds are typically and historically racked into oak foeders, while oud bruins get racked into stainless steel tanks for souring. Lambics are traditionally left on the yeast cake in oak barrels where the long aging process provides the bacteria and brett with nutrients from the autolysed yeast cells during aging. This helps sour the beer nicely.
With that being said, I have made great flanders reds/browns by racking off the primary after about 3-4 wks. and letting them age in carboys for extended periods of time. I have also made flanders reds w/o racking them off the primary and leaving them on the primary yeast cake in the same carboy for 18 mos, with no hints of yeast autolysis, but rather a very sour, well attenuated beer.
For most of my lambics, I will leave them in the primary on the initial yeast cake for the entire aging period until I add fruit or blend them. I will only rack them over if I plan to reuse the yeast for another batch. Both methods have worked well for me in sour beer production.
So, you can either be historically accurate or brew how you want to and both ways will yield good results. Good luck and most of all have fun with these beers!
