new billing plugin

I know that there are some threads about billing, but I would like to start a new one because the others have a lot of irrelevant information.

I want to construct a new (simple) billing plugin, but I would like to know if there are people interested, and which functionality the plugin should have.
I have a functionality list of my own (of course):
- reseller/ user DA package subscriptions
- reseller/ user other subscriptions (for example some consultancy hours)
- invoice creation for admin/ reseller (automatic or by hand)
- invoice notifications (invoice received, invoice not paid, etc.)
- invoice template (html and pdf)
- different currencies/ vats
- view send invoices for admin/ reseller
- view received invoices for reseller/ user

My questions:
- are if you are interested?
- what is the minimum functionality for the plugin?
- do you have any comments/ additions to my list of functionalities?
- would you like to see a paymentmethod part included? (like paypal)
- pricing? (amount, per year, per month, etc.)
- should the code be unencrypted? (so would you like be able to change the code yourself)

- Yes
- autom. invoicing / reminders on "not paid"
- not yet
- iDeal (dutch payment method) / banktransfer
- pricing of invoices on yearly/monthly basis & pricing of plugin: pay once.
- Yes i like to make changes to the code to fit my needs,
if you alreedy have some code i might be able to help you to develop it a bit further.

I do not have any code yet. I first want to see if it is worth it to construct such a plugin.
And I am already experienced with the iDEAL payment method (and integration), so that will not be a big problem.