My instinct would be to KISS the first time you use a significant new ingredient - worry about getting a feel for the yeast rather than getting too hung up on replicating the recipe too literally. So I wouldn't add the lactic, just see where you end up with Philly Sour on its own, seems there's a fair bit of scope for manipulating it by tweaking conditions.
Be interesting to hear how you get on with it - there's a
pretty good thread on HBT about it if you've not seen that.
[For those that haven't heard about it,
Philly Sour is Lallemand's dried
Lachancea species, a yeast that produces acid as well as fermenting so the pitch is you can make sours without messing about with bacteria.]