I recently did what you are doing. I cultured some pacman yeast from some bombers of rogue. I stepped up a few starters until I had a good amount of yeast in a half gallon starter. I let it ferment out, washed it, and split it into separate mason jars to use for future batches, ending up with what you have in the picture there. When I take them out of the fridge about 5 days before brewing, I make a weak 1 liter starter. When that one starts to ferment out, I pitch the slurry into another normal strength 1 liter starter and thats when it really goes nuts and I feel assured it will do the job. My last beer was a 1.076 OG and the yeast is doing its job well. Its hard to over pitch as a home brewer so you should be more concerned about under pitching. There are so many arguments about this and calculators that will help you figure out what size starter and how many yeast cells you need, but my method has always fully fermented my beer, usually ending up at 1.012 FG. Hope this helps.