G'day Mike,
Try something like this in a button script:
//Check to see if a min of 5 check boxes are completed on page 1
var selectedFields = [];
for (var i=0; i<this.numFields; i++) {
var f= this.getField(this.getNthFieldName(i));
//The page property defines the page that the fields are on
if (f.value=="Yes" && f.type=="checkbox" && f.page == "0"){ //Change the 0 to be the page no. where the check boxes are
selectedFields.push(f.name);}
}
if ( selectedFields.length >= 5 )
app.alert("Thanks, you have completed a minimum of 5 fields");
else
app.alert("You must complete a minimum of 5 fields");