How to remove the "my products" in the PayPal integration?

When I clicked Payments ... PayPal, it added a little "My Products" thingamajig to the form, even though I specified User-Defined and not selling products. Will that go away once I've established a PayPal account for this project?

You can rename the label if you do not want the "My Products" label.

Since you selected the user-defined type, the user must type the amount in the textbox of your payment field. What you can do is change its label.

Do I use a different form type or theme if I want the amount to automatically transfer from my calculation box to PayPal without the user having to type it in?

Also, I want to have two different submit buttons: one where there is a balance due, that goes to PayPal, and one that shows up when there is no balance due and only the form is submitted without going to PayPal. Is that a problem? I have used conditions to specify when the submit without payment button shows instead of the PayPal button.

No, you do not need to change your form type or the theme. You can pass the calculation to the payment field, guide below:

https://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field

You do not need to condition the submit button. Just show Paypal by its current condition. When people choose to Pay, they will be required to prepay since you are using the Paypal Checkout integration in the form. If no amount is due, the form should submit without requiring users to pay.

Lastly, don't forget to connect your Paypal account in the Paypal Checkout integration. I see it is not yet connected.