As with all sours, you've got time on your side...
If you like it sour, pitch the roselare on its own. If you want less pucker, pitch in the secondary after a clean, ale yeast in the primary.
Either way, if the level of sourness isnt to your liking, brew another batch using the opposite method and blend. After a few years of making sours, you'll be doing this anyway!
If this will be for a competition, I'd err on the side of more sour than less sour. Just like with bitterness in IPA, you usually need to be on the high side of the style for it to be perceived as "in-style" by the judges.
BJCP judges - please comment...