Can I create my own Theme and Design

Hello,

I am planning to create and deploy WordPress to my client’s site. Where WordPress is hosted on our own Windows Server with Apache Web server. I need to understand what are the implications commercial and otherwise we would encounter if we need the following on the blog:

1. Posts
– max number
2. Capacity to insert images, videos, etc
– max size if it is installed on my server
3. Preview post before publishing option
4. Allow various separate authors to make post – Max number of authors
5. Categories
6. Tags
7. Pages
8. A header or appropriate backgrounds and branding – Branding of my client’s Logo
9. A tag cloud
10. Subscription facility
11. Comments facility
12. Approval for comments before comments go live
13. Capacity to install free widgets – like a date stamp, tweet this, make a fb update about this, etc

There was a link I found in wordpress.com which mentions some charges for adding more themes and max size etc, but as we are deploying it in our server does this restriction hold true?

Thanks and Regards,
Sunil Rao