I just posted a thread touching on this subject in the yeast sub-forum.
My experience with 5335 is that you will know if your starter has been successful based on the smell and taste of the starter liquid. When it works, it tastes/smells clean and sour; when it doesn't work, it looks/tastes/smells like crap, as a result of something other than lacto working away. There are testimonials of successful lacto-soured beers that started off smelling like vomit, but since you're using a pure culture you should be able to avoid that.
I've had the best luck keeping the wort in the upper-80s/lower-90s. Although I hear that simple sugars are better for doing a lacto starter (i.e. cider), I have had great results using a standard starter wort. Using a mason jar, I pressed some syran wrap over the surface of the wort, covered the mouth of the jar with tin foil, let it sit and a few days later, I had a nice sour starter.
Apart from low temperatures, I would recommend stepping up your starter more gradually than you would a normal yeast starter. By that, I mean start with 500ml of liquid, then pour all of that into a larger container with another 500-1000 ml of starter liquid. I'm not sure how well the bacteria will crash out, but since you're going for a sour beer anyways, I would pitch the entire resulting starter.
Lastly, make sure that the starter is active when you pitch it. This is based on personal experience, but the less lag time the better.