I would make a starter with the Lacto (low gravity, no oxygen, keep it hot). As long as it is going strong you should be fine (not sure if the ratio refers to cell count or volume or what). Keep the IBUs low, too many IBUs stop Lacto and cause most of the Berliner problems I hear about.
I would wait longer than Kristen suggests before bottling, but then I'm a bit of a nervous guy when it comes to sour beers. I also like a hint of funk in my Berliners, so I add some Brett and give then a few months before bottling.