Query on themes.

HI all,

I have a requirement from my client, Saying he needs CMS and Social Network, Needs to be under one domain, Is there any possible way of doing it ?? If so how ??

What in my mind is, Can i do like this!

1) I will buy a parent theme where i can do all the CMS work
2)Similarly i thought will buy a child theme, and integrate with Parent theme??

Is it a good idea ? will this work ??
if it sounds like a good idea, Please suggest me with a demo theme, So that i can test on that then decide on spending some money on buying a theme.

If not how can i deal with this.

Please suggest me.