Building a stream status website

Hello, I'm a newbie to wordpress and novice of building a website, so I need some guilds and advises in order to kick start.
I am building a site that for visitors to register/login and post their statues (the site concept is for members put their status or img (only) on my site, nothing else, no blogs, no other pages), with registered member's profile. like a very simple tweeter. My questions are:
1. Do I need a Buddypress first in order to use other plugin?
2. Any live stream status plugin you would suggest?
3. What do I need for vistor to register/sign in
4. I want the public home page is a register/sign in request page in order to get in to the live stream status page.

Last, Thanks to read my questions. I am looking forward to hear from you. Thank you.