When doing crunch and other ab exercises, am I suppose to do a certain amount of reps like when working my arms and legs etc. or are crunches different where I should just keep doing it until they burn and can't do any more? And how often a day or week?

Do the crunches to the burn and no further, but keep track of how many that is up to that point and don't go beyond until you can do more easily.

Tick

Abs are a muscle group like any other. Work them the same way. Add weights to add resistance if necessary and work to near failure. Then give them time to recover before you do it again.

How long to recover? Within a day or skip a day?

If you are hitting them really hard, you might need several days. Think how your legs feel after a heavy squat session, and how long they need to recover. You should be hitting your abs that hard, and giving them the same sort of time.

Sense I'm already toned, should I be doing less reps and use a dumbbell, or should I just do it the normally way without weights and do as many as I can it until it burns?

I'd add a weight, or change the exercise to make it more difficult. Try V-ups instead of crunches, or do kneeling crunches using a weight stack, things like that.