To enhance my web based services/application further, I want to develop
add-in
for outlook, here is a brief on what it will be like

1) it will have a button somewhere on outlook main toolbar
2) and on mail composing toolbar as well
3) when the button is clicked it will open up a form (or multiple forms) to
take
  further input from user.
4) and based on input will compose the email automatically
5) finally queue it up for sending

I am advance level c# developer but am new to office developments, I saw a
lot of
articles on internet on how to do what I need, but before diving into the
coding I would
like to confirm a few general questions (to be on the safe side) and will
appreciate
the replies from everyone in general and office/outlook MVPs in particular.
Please
provide any authentic references if you have them handy.

1) Do we have to pay anything to Microsoft for developing the addin or for
  distributing/selling the addin ?

2) Do I have to qualify in some way, or does my technology needs to ?

3) What are the allowable areas of functionality that one can add ?
  any limitations that you would like to highlight compared to a standard
  win forms app.

4) What are the ground rules for integrating with Outlook?

I am excited and eager to hear back from you guys, please guide.

Thanks,
Farhan