Well, being a Thompson fan,

Belts should be worn with kilt, but not with westcoat. If worn with westcoat, then westcoat should be tucked under belt.

Tried it both ways, best without belt.

Belt loops are not for belt but sporran.

But since Scots tend to be notoriously independent, i.e., if they don't have anyone else to fight, they will fight each other, whatever you think looks good and is in good taste.