The couscous in Roasted Mediterranean Salad

Hello Lindsey, I'm making Delia's Roasted Mediterranean Vegetable Cous-cous salad over the weekend but I can't source the medium cous-cous, only very fine or the giant wholewheat variety (which requires 6-8 mins cooking). As I've nrver cooked with couscous, which do you recommend for this recipe and if it's the giant variety, can I cook it ahead?

Thank you.

Eileem