Planned Mysql Cluster on different Dedicateds consultancy & Set up

We made a social networking site which is similar to many known ones. We used nodejs on coding which we believe its fastness. We need help to get project grow to multi millions users. Hopefully it will be one of the best social network. So we need to plan and do solve estimated problems such as mysql queries bogged after several millions of users. We have heavy selections for users. We ask to let us know best hosting enviroment such as cloud hosting to grow our database or how to use more than 4 machines with mysql clustering. We can buy 4-5 dedicated machines without problem. Which it can grow to hundreds or more machines when needed. shortly help and asistance on our 3 years worked project. We no use apache or php for this reason acunu or apache cassandra is not an option for us.