Regarding usage and licenses [ Edited ]

[nbl_lb]

I have some questions regarding cost of developing an application using Force.com as a platform instead of some other. This site will need to lookup SalesForce data for some of its functions and reports. Specifically  my questions are:

1. If I have 5 developers working on an application called XYZ using Force.com, how many Force.Com licenses would I need to purchase for such development work and of what type should those licenses be? How many SalesForce.com licenses should I need to buy?
2. Can I reuse those same licenses for the testing phase later?
3. If my XYZ application needs to pull some data off SalesForce then do I need one additional SalesForce license or do  I need to get one license per login/user that my site XYZ would have?
4. If my XYZ application has 10 internal users who are site administrators for XYZ and 200 external users who generally use the site, then how many licenses do I need to buy of Force.com and how many of SalesForce?
5. If I want to develop and deploy an application on Force.com that uses SalesForce data will it be sufficient if I only use one Platform license for accessing SF data between all the developers who are working on the Force platform using their Force.Com developer licenses?
6. Once development is complete how many platform licenses will the application deployed on Force.com need to serve n number of users accessing the website?
7. Once development is complete how many platform licenses will the application deployed on our own hosting provider and not Force.com need to serve n number of users accessing the website ?

Im not sure if this is the right place to ask questions of this type, so incase there is a better place can the moderator move my questions there?

Thanks.