IIRC, you posted a pic of your husband in another thread, and there were recommendations that he wear the kilt higher (or I may be thinking of somebody completely different, sorry if that's the case!). Fellows with bellies can have that problem, as the kilt wants to slide down to the smaller circumference at their hipbones. Pulling the kilt up so that the larger circumference of belly is below the waistband helps keep it from sliding down, but of course it needs to be the right length for that placement.

Yes, the velcro is just to keep it closed, and to keep the underapron from sagging down below the hem of top apron. Straps perform the same function. I've seen one modern/casual kiltmaker who doesn't put any closure on her kilts at all, instead figures that the belt will keep them in place. Not so sure about that one. . . she does offer closures if the customer requests.