How one should understand whether he is really ready to have his own social network?
If you have a positive answer on any of the following questions, you should start your network:

• I have an original idea and I’d like to unite a circle of like-minded persons, but I need options of control over behavior of the community members.
• I have an original idea, which would be popular among certain people, and I’d like to join them and to earn some money with that.
• I think that I have sufficient funds, and if I invest them into social network, I’ll be able to make it popular or the audience I’m interested in.
• I need it for a leisure or as a hobby
• I “just really want it” 

So, to finalize that, in order for your project to be successful, you should either have an original idea the people would “move for”, or have sufficient funds to make your network popular (internet advertisement, search optimization), or just really want it.