New PayPal Custom Payment Gateway

We are having some problems with our PayPal accounts and as we bought your plugin licence for the invoice part, maybe we could use it also for the payment gateway.
What we want to do:
We have 2 PayPal accounts: one for small amounts and one for bigger ones. We would like to be able to redirect to one or the other depending on the cart total amount.

What we could do:
I understand that we could use the min/max amounts payment gateway. We could use the WooCommerce PayPal default for one account and then we just need to have another one for the second account. Is it correct?

The problem: How do we create a custom payment gateway? We were able to create all the specifications except that we don’t find where we can insert all the PayPal information. We are not really able to understand how to define what the gateway has to do, where is the code of the gateway.

What do you think? Is it possible to do something similar with your plugin? Any ideas about it?

Thanks in advanced.-