Those WY Roselare packs are just fine to pitch alone for 5 gallons. No starter needed. Don't get freaked out if the beer takes 48 hrs to get going in this fashion. It will be okay in the long run. No worries. If it were me, I probably would not even aerate the beer, just a little splashing when transferring to the carboy is enough.
Don't be afraid to pitch the dregs of a couple bottles of commercial sour beers either as the WY Roselare blend, as good as it is, can still be quite tame and take at least 12-18 mos to produce enough acidity on its own.
Repitching this strain in successive generations will lead to a faster, more robust sourness in less time, so if you are interested when you rack the beer into secondary for long term aging brew another beer on the same day and pitch a cup or two of the yeast cake into the new cooled batch. Let the good times roll!