nitinjindal
The load for the software doesn't really matter, this all mainly depends on the server itself. You will need to ensure your server(s) can handle such load and can be easily scalable as the more data and more traffic you get the harder the software/server has to work (with limited resources).
An ideal initial setup for such a large system would be to setup two webservers with load balancing (like HaProxy and NGINX/Apache), two or more MySQL databases using galera cluster (replication + high availability/failover), ProxySQL for splitting the load for SQL reads/writes, and installing either the Attachments on the Filesystem plugin or the Attachments in S3 plugin so all the attachments are stored outside the database to keep the database size optimal. With that setup it should be a long while before you had to do any scaling (if ever). There are other things you can do as well such as optimizing MySQL, etc. but that's a whole separate thing.
I hope this provides some clarity.
Cheers.
