Presumably you don't need to set the subform to "hidden" if you also have a min count of 0. No instances will be created until your button is clicked (on some other page) that does form1.Subform1.instanceManager.addInstance(1);
Setting the subform visible should do the trick, if you choose to initially set it to hidden. Your script to show the subform was:
form1.Subform1.presence = "visible";
That script is only going to set the first instance of the subform to visible; it's equivalent to Subform1.presence = "visible"; You may need to update your script to use the index of the instance of the subform that you just added. (Still, I think in this case you don't really need to set the subform to hidden, to begin with).
Note that you only need to call recalculate() if you're targetting older versions of Acrobat; maybe earlier than 7.1?
I posted some (hopefully useful) information on this topic on a blog that i recommend you read: