Requirement to setup site to sell wordpress theme

Hi all,

I’m completely a newbie when comes to setup a site to sell wordpress theme.

My requirement:

1. I would like to setup a simple shop to sell wordpress theme which user to upgrade theme after they purchase a theme.

2. Purchase only can be made after user register the site or register during purchasing a theme.

3. Login a must to purchase.

4. Purchase using paypal

5. User can access forum for theme issues, suggestion and so on.

For short term, I just want to trial run the site. No need member to upgrade membership to get all themes.

For long term, yes. I would like member to upgrade membership to get all theme.

Questions:

1. What theme should I use?

2. Theme demo, do I need to a separate theme demo or use plugin? I would like to see the demo site with purchase button.

3. What plugin compatible with theme suggested.

Hopes you all have some hand on this.

Rozani