Next to your normal user table \"user\"(user_id/user_email/user_pwd/etc), what is the best way to go to store profile information?
Would one just add fields to the user
You need way more than 3 tables. How will he store data like multiple emails, multiple addresses, multiple educational histories, multiple "looking for" relationships, etc. Each needs its own row assuming many values will be lookups like city, sex preference, school names, etc. so either normalize it fully or go the noSQL route, no point in hanging in the middle, you will lose the best of both worlds.
you can duplicate rows but it wont be good. social networks do not live with 50,000 users. either you will be successful and have millions of users or you will crash and clsoe it because to run these you need $$$ which will only come if you have a solid user base. With only 50,000 users for life investors wont invest, ad revenues wont cover the cost and you will close it. So design it like you want to be the next facebook right from day one. Think big!