How can I test the plugin?

Good evening, I live in Brazil, and I have some doubts about the plugin, I would like to know how I make the mass payment by paypal, how much does it cost to do this? and I would like to know for a project further on, if there is no way I enter the plugin code and add another payment method of its own with the option to split, because I know how to program, and I want to add the functionality of the market paid split. Another doubt, how can I test the plugin? how can I test the payment to the suppliers, by paypal in bulk. In case I want to use Stripe, does it split the purchases? if yes, how can I activate this, and have how to pass the rates to the buyer? In the case of the payment gateway fee, I want it to be charged on top of what I’m going to get from my seller, for example, the seller will get 85% and I’ll get 15%, but the gateway charges 5%, I want it to be taken out of 5% of my 15%.