When you buy a Prince Charlie rig you do not normally get a belt with it. Likewise in military rig if you're wearing a waist coat you don't wear a belt.

If you have a Argyll Jacket a belt would be appropriate. This is the type of Rig I'd suggest wearing to your "hot" wedding if you don't choose something more casual

I have a huge kilt which is far too big if I have to wear it with a waistcoat I'll wear braces so it doesn't fall down, I wouldn't consider wearing a belt.

At he end of the day its not something to get anal over, if you can, try both a YOU decide what looks best