Currently you can add a custom payment if the payment system supports POST or GET request.
I don’t think I have work with the methods that you mention above, but if you can provided links or some documentation I will see what I can do for feature releases.
Bank transfer and on demand payment options are same. On bank transfer method customer should checkout after finishing an adress form. After applying form one mail to customer for “thank you and bank transfer info” and one mail to webmaster.
On Demand options is the same. It just to show customers we have that payment options.
Hi again, i forget to write this; customers can select payment options in any list. 2 or 3 payment options have to showing on the same time to customers.