Should I be enqueueing styles/scripts once and then dequeueing them?

dequeue means it should be removed from the queue. All the scripts in the queue get loaded at page load.
Once the page is loaded, you cannot use dequeue to remove the script.

Best is to only load the scripts you really need. You might load it conditionally in the constructor based on which page is loaded. In your case, the page(s) with the paymentform on it.
Hope this helps.