Is it proper to build a site supporting blog visitors in WordPress?

Maybe you need to use the WordPress Network feature

Documentation of interest:

EDIT:
Some features of WordPress Multisite based on my investigation:

1 Users can register a blog in your site and publish their pages.

2 Users can embed images, audios and videos in their pages.

3 Users can customize the theme of their blogs.

4 Users can create polls in their pages. (A question and a list of answers)

5 Blog visitors can respond to a blog by comments or by answering the owner’s questions.

6 Users can create/delete a list of visitors for their blog. Visitors should have basic infomation such as name, email and auto-generated passcode. (For example, a blog owner might want someone to enter a passcode to view a certain page of his blog)

To get started and to learn more, go HERE

Also, check out BuddyPress, a WordPress plugin that will allow you to build your own Social Network