An ID isn't necessary for a button to work, it is by design that the eCart did not add one. to hide or show the button, an id needs to be added.
in the example code above, there is already code to hide or show the button, based on the ID "LEDCart_1_ATCButton":
document.getElementById("LEDCart_1_ATCButton").style.display = "none"
your form uses the id LEDCart_1_ATCButton, so the button ID needs to be unique. in the code i used LEDCart_1_ATCButton
To limit the quantity that can be added to the cart, you would need to have another column in the cart object for available quantity. In the add to cart button, store the available quantity for the item. then you can create a calculation that rests the quantity to the available quantity if the user tries to add a value above it, for example:
abs([Quantity] > [AvailableQuantity])?[Quantity] = [AvailableQuantity]:''