here's a thread that might help:
sounds like you're doing everything well. i can't answer the question about cold crashing lacto, though. i'm not sure, but it sounds like that would work fine. i typically just pitch the whole starter, but that's me and i'm not as anal as a lot of people when it comes to certain procedures.
in the lambic & wild brewing section there are alot of threads about lacto. after searching for lacto cold crash i came up with this thread that loosely states lacto won't cold crash. or at least that's what i make of it: http://www.homebrewtalk.com/f75/strawberry-alarm-clock-v3-0-strawberry-blonde-132129/
Started cold crash from room temp (~72F). Used frozen PET water bottles and ~1LB ice blocks from tupperware to bring cooler temp down, swapping out when ice is depleted.
morning temp is 41F, added 4 ice blocks + 8 PET bottles, by afternoon temp was at 35F and held steady.
morning temp went back up to 40F overnight, but quickly cooled to 35.
temp still at 35F, pulled out of cold bath and transferred to bottling bucket at 3:30pm.
There was a very thin white layer of what looked like possible lactobacillus floating on surface of fermenter, but no off flavors whatsoever."