Plugin Recommendation

What plugins should I be looking at in order to quickly achieve a working prototype?

The WordPress plugin community is quite large and overwhelming for a new comer like me. I would like to have some suggestions from experience WordPress user on what plugins should I consider in my analysis phase of my project.

Plugin criteria:

• Good quality. Somewhat mature in a sense that I won’t be slowed down by bugs and lack of documentation.
• Easy to use. Intuitive and good flow.
• Integration ready. Can interact with other plugin when it make sense.
• Low cost. Free plugin is preferable but I can settle on paid plugin if the ROI is good.

Short term needs:

• Membership content only. The entire site must be protected with an authentication except for a landing page explaining what is going on.
• Gather email for membership invitation. The landing page is used to gather email for as needed invites.
• Members can post. Pretty straight forward.
• Other members can improve any post. The tricky part about posting is that any other members can edit any other post. Kind of like a wiki.
• User posts follows a hard layout. All post needs to have certain fields present and filled.
• Discussion can take place for each post.
• Post can be tagged and categorized.
• Different style of voting for each post. A member can vote up or down a post but it can also “+1” a post.
• Custom RSS feeds creation by the user. A member can create a custom RSS feed with different filters on post author, voting, categories, tags, etc. It can be mix and matched.

Longer term needs:

• Adjustable monthly paid subscription. A based subscription is enforced with a per user discount if needed.
• User can invite people to join the membership.
• Discussion on post can be watched for moderation.

Thanks for your help and don’t hesitate to ask for more details on my requirements.