Hi,
1. It's a vendor restriction. If you select "none", it means no vendor restriction and thus it applies to all the vendors.
2. That won't be the case if you remove the "payment" view form the "checkout workflow" as you said you had in your first message.
3. You would have to edit the file "pay" of the view "order" via the menu Display>Views and add such code at the begining:
<?php
$this->order->order_payment_method->order_payment_method = 'paypal';
$this->order->order_payment_method->order_payment_id= XXX;
?>
where XXX is the id of your payment method in the menu System>Payment methods.